diff --git a/src/cljam/cigar.clj b/src/cljam/cigar.clj
index bd22ec53..1ca5d2c3 100644
--- a/src/cljam/cigar.clj
+++ b/src/cljam/cigar.clj
@@ -8,6 +8,45 @@
   (for [[_ n op] (re-seq #"([0-9]*)([MIDNSHP=X])" s)]
     [(Integer/parseInt n) (first op)]))
 
+(defn simplify
+  "Merge contiguous same operations of parsed CIGAR."
+  [cigs]
+  (loop [[[^long l op :as x] & xs] cigs result (transient [])]
+    (if (and l op)
+      (let [[^long nl nop] (first xs)]
+        (if (= op nop)
+          (recur (cons [(+ l nl) op] (next xs)) result)
+          (recur xs (conj! result x))))
+      (persistent! result))))
+
+(defn- concat! [v coll]
+  (reduce conj! v coll))
+
+(defn- update-last! [coll f]
+  (let [c (dec (count coll))]
+    (if (neg? c)
+      coll
+      (let [[op x] (get coll c)]
+        (if (= :m op)
+          (assoc! coll c (f x))
+          coll)))))
+
+(defn to-index*
+  "Convert CIGAR string to sequence of indices."
+  [^String s]
+  (let [cigs (simplify (remove (comp #{\P \H} second) (parse s)))]
+    (loop [[[^long l op] & xs] cigs r 0 s 0 idx (transient [])]
+      (if (and l op)
+        (condp get op
+          #{\M \= \X} (recur xs (+ l r) (+ l s) (concat! idx (map (fn [x] [:m x]) (range s (+ l s)))))
+          #{\D} (recur xs (+ r l) s (concat! (update-last! idx (fn [x] [:d x (range r (+ l r))])) (repeat l [:m \*])))
+          #{\N} (recur xs (+ r l) s (concat! idx (repeat l [:m \>])))
+          #{\S} (recur xs r (+ s l) idx)
+          #{\I} (recur xs r (+ s l) (update-last! idx (fn [x] [:i x (range s (+ l s))]))))
+        (persistent! idx)))))
+
+(def to-index (memoize to-index*))
+
 (defn count-op
   "Returns length of CIGAR operations."
   [^String s]
diff --git a/src/cljam/cli.clj b/src/cljam/cli.clj
index 0601bebb..e0bafa7b 100644
--- a/src/cljam/cli.clj
+++ b/src/cljam/cli.clj
@@ -244,7 +244,7 @@
                                         :seq (cstr/join (% line))
                                         (% line)) [:rname :pos :ref :count :seq :qual]))))))
   ([rdr rname start end]
-   (doseq [line  (plp/mpileup rdr rname start end)]
+   (doseq [line  (plp/mpileup nil rdr rname start end)]
      (if-not (zero? (:count line))
        (println (cstr/join \tab (map #(case %
                                         :qual (cstr/join (% line))
diff --git a/src/cljam/pileup/mpileup.clj b/src/cljam/pileup/mpileup.clj
index a405a18d..3e89f0c6 100644
--- a/src/cljam/pileup/mpileup.clj
+++ b/src/cljam/pileup/mpileup.clj
@@ -7,72 +7,77 @@
             [cljam.sequence :as cseq]
             [cljam.io :as io]
             [cljam.fasta :as fa]
+            [cljam.cigar :as cig]
             [cljam.pileup.common :refer [window-width step center]]
             [cljam.pileup.pileup :refer [rpositions]]))
 
-(defn- append-seq
-  [op target current]
-  (case op
-    \M (apply conj current (map str (:seq target)))
-    \I (if (seq current)
-         (update-in current [(dec (count current))]
-                    vector
-                    (str "+" (:n target) (apply str (:seq target))))
-         current)
-    \D (apply conj current (map str (:seq target)))
-    \N (apply conj current (map str (:seq target)))
-    current))
+(defn to-mpileup
+  "Stringify mpileup sequence."
+  [x]
+  (if (vector? x)
+    (let [[y op xs] x] (apply str y op (count xs) xs))
+    (str x)))
 
-(defn encode-seq [seq*]
-  (loop [[f & r] (filter #(nil? (#{\P} (:op %))) seq*)
-         ret     []
-         op      nil
-         tmp     {:n 0, :op nil, :seq nil}]
-    (if (nil? f)
-      (append-seq op tmp ret)
-      (if (nil? op)
-        (recur r ret (:op f) f)
-        (if (= (:op f) op)
-          (recur r ret (:op f) (-> tmp
-                                   (update-in [:n] + (:n f))
-                                   (assoc :op (:op f))
-                                   (update-in [:seq] (partial apply conj) (:seq f))))
-          (let [new-ret (append-seq op tmp ret)]
-            (recur r new-ret (:op f) f)))))))
+(defn substitute-seq
+  "Substitute sequence with mpileup index."
+  [[^Character r & refs] ^String s [op x xs]]
+  (letfn [(get-char [i] (if (number? i) (let [c (.charAt s i)] (if (= c r) \. c)) i))]
+    (case op
+      :m (get-char x)
+      :d [(get-char x) \- (take (count xs) refs)]
+      :i [(get-char x) \+ (map #(.charAt s %) xs)]
+      x)))
+
+(defn substitute-qual
+  "Substitute base quality with mpileup index."
+  [^String q [op x]]
+  (if (and (number? x) (not= q "*")) (.charAt q x) \~))
 
 (defn pileup-seq
   "Returns a lazy sequence that each element contains reads piled-up at the locus."
   [^long start ^long end reads]
   (letfn [(cover-locus? [pos aln]
-            (<= (:pos aln) pos (sam-util/get-end aln)))
-          (step [[pos buf alns]]
-            (let [[i o] (split-with (partial cover-locus? (inc pos)) alns)]
-              [(inc pos) (concat (filter (partial cover-locus? (inc pos)) buf) i) o]))]
-    (map second (rest (iterate step [(dec start) [] (remove (comp empty? :cigar) reads)])))))
+            (<= (:pos aln) pos (:end aln)))
+          (step [pos buf alns]
+            (lazy-seq
+             (when (< pos end)
+               (let [[i o] (split-with (partial cover-locus? (inc pos)) alns)
+                     b (doall (concat (filter #(<= (inc pos) (:end %)) buf) i))]
+                 (cons b (step (inc pos) b o))))))]
+    (->> reads
+         (sequence
+          (comp
+           (remove #(and (empty? (:cigar %)) (nil? (:cigar-bytes (:meta %)))))
+           (map #(assoc % :end (sam-util/get-end %)))
+           (drop-while #(< (:end %) start))))
+         (step (dec start) []))))
 
 (defrecord MPileupElement [^String rname ^long pos ^Character ref ^long count seq qual reads])
 
-(defn- gen-mpileup
+(defn gen-mpileup
   "Compute mpileup info from piled-up reads and reference."
-  [^String rname ^long locus ^Character reference reads]
-  (let [seq (mapv (fn [{:keys [^long pos ^String seq ^String cigar] :as aln}]
-                    (let [s (nth (encode-seq (cseq/parse seq cigar)) (- locus pos))]
-                      (cond
-                        (vector? s) (second s)
-                        (= reference (first s)) "."
-                        :else s))) reads)
-        qual (mapv (fn [{:keys [^long pos ^String qual] :as aln}]
-                (if (= qual "*") \~ (nth qual (- locus pos) \~))) reads)]
-    (MPileupElement. rname locus reference (count reads) seq qual reads)))
+  [^String rname ^long locus [^Character ref-base :as refs] reads]
+  (let [seqs (map (fn gen-mpileup-seq [{:keys [^long pos ^String seq cig-index]}]
+                   (substitute-seq refs seq (nth cig-index (- locus pos)))) reads)
+        qual (map (fn gen-mpileup-qual [{:keys [^long pos ^String qual cig-index]}]
+                    (substitute-qual qual (nth cig-index (- locus pos)))) reads)]
+    (MPileupElement. rname locus ref-base (count reads) seqs qual reads)))
 
 (defn pileup*
-  "Internal pileup function independent from I/O."
-  [refseq alns rname start end]
-  (map
-   (partial gen-mpileup rname)
-   (range start (inc end))
-   refseq
-   (pileup-seq start end alns)))
+  "Internal mpileup function independent from I/O.
+   Can take multiple alignments seqs."
+  [refseq rname start end & aln-seqs]
+  (->> aln-seqs
+       (map
+        (fn [alns]
+          (->> alns
+               (sequence (map (fn [a] (assoc a :cig-index (cig/to-index (:cigar a))))))
+               (pileup-seq start end))))
+       (apply map
+              (fn [index refs & plps]
+                (map (fn [plp] (gen-mpileup rname index refs plp)) plps))
+              (range start (inc end))
+              (partition 10 1 (concat refseq (repeat \N))))))
 
 (defn pileup
   "Returns a lazy sequence of MPileupElement calculated from FASTA and BAM."
@@ -89,7 +94,7 @@
                       (fa/read-sequence fa-reader {:chr rname :start s :end e})
                       (repeat \N))
              alns (io/read-alignments bam-reader {:chr rname :start s :end e :depth :deep})]
-         (pileup* refseq alns rname s e)))
+         (map (fn [p] (update (first p) :seq (fn [s] (map to-mpileup s)))) (pileup* refseq rname s e alns))))
      (catch bgzf4j.BGZFException _
        (throw (RuntimeException. "Invalid file format"))))))
 
diff --git a/test/cljam/t_cigar.clj b/test/cljam/t_cigar.clj
index 8cce60fa..3218f3b4 100644
--- a/test/cljam/t_cigar.clj
+++ b/test/cljam/t_cigar.clj
@@ -4,3 +4,39 @@
 
 (fact "about parse"
   (cgr/parse  "1S2I6M1P11I") => '([1 \S] [2 \I] [6 \M] [1 \P] [11 \I]))
+
+(tabular
+ (fact
+  "cigar to index"
+  (map (fn [[op x :as xs]] (if (= op :m) x xs)) (cgr/to-index* ?cigar)) => ?index)
+ ?cigar               ?index
+ "4M"                 [0 1 2 3]
+ "1M3I"               [[:i 0 [1 2 3]]]
+ "1M3D"               [[:d 0 [1 2 3]] \* \* \*]
+ "2M3I"               [0 [:i 1 [2 3 4]]]
+ "4D5M"               [\* \* \* \* 0 1 2 3 4] ;; ^]* * * * A T G C A$
+ "4D5I"               [\* \* \* [:i \* [0 1 2 3 4]]] ;; TODO: ^]* * * *+5TGCA=$
+ "4S4M"               [4 5 6 7]
+ "4H4M"               [0 1 2 3]
+ "1M3I1M"             [[:i 0 [1 2 3]] 4]
+ "2M3I1M"             [0 [:i 1 [2 3 4]] 5]
+ "4I2D5M"             [\* \* 4 5 6 7 8] ;; ^]* * A T G C A$
+ "1M4D5I"             [[:d 0 [1 2 3 4]] \* \* \* [:i \* [1 2 3 4 5]]] ;; TODO: ^]* * * *+5TGCA=$
+ "1M3D3M"             [[:d 0 [1 2 3]] \* \* \* 1 2 3]
+ "1M2D1I2M"           [[:d 0 [1 2]] \* [:i \* [1]] 2 3] ;; TODO: ^]A-2NN * *+1G G C$
+ "1M2N1I2M"           [0 \> [:i \> [1]] 2 3] ;; TODO: ^]A > >+1G G C$
+ "1M1I2D2M"           [[:i 0 [1]] \* \* 2 3] ;; ^]A+1T * * G C$
+ "1M1I2N2M"           [[:i 0 [1]] \> \> 2 3] ;; ^]A+1T > > G C$
+ "1M4I2D5M"           [[:i 0 [1 2 3 4]] \* \* 5 6 7 8 9] ;; ^]A+4TGCA * * C A T G C$
+ "1S4I2D5M"           [\* \* 5 6 7 8 9] ;; ^]* * T G C A T$
+ "3M2P2I3M"           [0 1 [:i 2 [3 4]] 5 6 7] ;; ^]A T G+2CA T G C$
+ "1P4I1D5M"           [\* 4 5 6 7 8] ;; ^]* A T G C A$
+ "5M1D3M4S"           [0 1 2 3 [:d 4 [5]] \* 5 6 7] ;; ^]A T G C A-1N * T G C$
+ "5M1N3M4S"           [0 1 2 3 4 \> 5 6 7] ;; ^]A T G C A > T G C$
+ "3H2S3M1D2S4H"       [2 3 [:d 4 [3]] \*] ;; ^]G C A-1N \*$
+ "1M1P1I1P1I2M"       [[:i 0 [1 2]] 3 4] ;; ^]A+2TG C A$
+ "2M1I1D2I2D1M"       [0 [:i 1 [2]] [:i \* [3 4]] \* \* 5] ;; TODO: ^]A T+1G *+2AT * * T$
+ "1S2I6M1P1I1P1I4M2I" [3 4 5 6 7 [:i 8 [9 10]] 11 12 13 [:i 14 [15 16]]] ;; ^]C A T G C A+2TG C A T G+2CA$
+ "6M14D1I5M"          [0 1 2 3 4 [:d 5 [6 7 8 9 10 11 12 13 14 15 16 17 18 19]] \* \* \* \* \* \* \* \* \* \* \* \* \* [:i \* [6]] 7 8 9 10 11]  ;; ^]A T G C A T-14NNNNNNNNNNNNNN * * * * * * * * * * * * * *+1C C A T G C$
+ "6M14N1I5M"          [0 1 2 3 4 5 \> \> \> \> \> \> \> \> \> \> \> \> \> [:i \> [6]] 7 8 9 10 11] ;; ^]A T G C A T > > > > > > > > > > > > > >+1C C A T G C$
+ "1S2M2D3M1D4M3D2M3D3M3I4M3D2M3S" [1 [:d 2 [2 3]] \* \* 3 4 [:d 5 [7]] \* 6 7  8 [:d 9 [12 13 14]] \* \* \* 10 [:d 11 [17 18 19]] \* \* \* 12 13 [:i 14 [15 16 17]] 18 19 20 [:d 21 [27 28 29]] \* \* \* 22 23])
diff --git a/test/cljam/t_pileup.clj b/test/cljam/t_pileup.clj
index 371e10d1..7c001466 100644
--- a/test/cljam/t_pileup.clj
+++ b/test/cljam/t_pileup.clj
@@ -3,22 +3,30 @@
         cljam.t-common)
   (:require [cljam.bam :as bam]
             [cljam.fasta :as fa]
-            [cljam.pileup :as plp]))
+            [cljam.pileup :as plp]
+            [cljam.pileup.mpileup :as mplp]))
 
 (def test-bam-pileup-ref '(0 0 0 0 0 0 1 1 3 3 3 3 3 3 2 3 3 3 2 2 2 2 1 1 1 1 1 1 2 2 2 2 2 1 1 1 2 2 2 2 1 1 1 1 1))
 (def test-bam-pileup-ref2 '(1 2 2 2 2 3 3 3 3 4 4 5 5 6 6 6 6 6 6 6 5 5 4 4 4 4 4 3 3 3 3 3 3 3 2 1 0 0 0 0))
 (def test-bam-mpileup-seq-ref
-  '(() () () () () () ("T") ("T") ("A" "A" "A") ("G" "G" "G") ("A" "A" "C") ("T" "T" "T")
-    ("A" "A" "A") ("+4AGAG" "+2GG" "A") ("G" "G") ("A" "A" "A") ("T" "T" "T") ("A" "+2AA" "A")
-    ("*" "G") ("C" "C") ("T" "T") ("G" ">") (">") (">") (">") (">") (">") (">") (">" "T") (">" "A")
-    (">" "G") (">" "G") (">" "C") (">") ("+1C") ("T") ("C" "C") ("A" "A") ("G" "G") ("C" "C")
-    ("G") ("C") ("C") ("A") ("T")))
+  '(() () () () () () ("T") ("T") ("A" "A" "A") ("G" "G" "G") ("A" "A" "C") ("T" "T" "T") ("A" "A" "A")
+    ("A+4AGAG" "A+2GG" "A") ("G" "G") ("A" "A" "A") ("T" "T" "T") ("A-1N" "A+2AA" "A") ("*" "G") ("C" "C")
+    ("T" "T") ("G" ">") (">") (">") (">") (">") (">") (">") (">" "T") (">" "A") (">" "G") (">" "G") (">" "C")
+    (">") (">+1C") ;; adjacent indel >+1T
+    ("T") ("C" "C") ("A" "A") ("G" "G") ("C" "C") ("G") ("C") ("C") ("A") ("T")))
 (def test-bam-mpileup-seq-ref2
-  '(() () () () () () (".") (".") ("." "." ".") ("." "." ".") ("." "." "C") ("." "." ".")
-    ("." "." ".") ("+4AGAG" "+2GG" ".") ("." ".") ("." "." ".") ("." "." ".") ("." "+2AA" ".")
-    ("*" ".") ("." ".") ("." ".") ("." ">") (">") (">") (">") (">") (">") (">") (">" ".") (">" ".")
-    (">" ".") (">" ".") (">" ".") (">") ("+1C") (".") ("." ".") ("." ".") ("." ".") ("." ".")
-    (".") (".") (".") (".") (".")))
+  '(("A") ("G" "G") ("G" "G") ("T" "T") ("T" "T") ("T" "T" "T") ("T" "T" "T") ("A" "A" "A") ("T" "T" "T")
+    ("A" "A" "A" "C") ("A" "A" "A" "A") ("A" "A" "A" "A" "A") ("A" "A" "A" "A" "A") ("C" "C" "C+4AAAT" "T" "T" "T")
+    ("A" "A" "A" "A" "A" "A") ("A" "A" "A" "A" "A" "A") ("A" "A" "T" "T" "T" "T") ("T" "T" "T" "T" "T" "T")
+    ("A" "A" "A" "A" "A" "A") ("A" "A" "A" "A" "A" "A") ("T" "G" "G" "G" "G") ("T" "T" "T" "T" "T")
+    ("C" "C" "C" "C") ("T" "T" "T" "T") ("A" "A" "A" "A") ("C" "C" "C" "C") ("A" "A" "A" "A") ("G" "G" "G")
+    ("A" "A" "A") ("G" "G" "G") ("C" "C" "C") ("A" "A" "A") ("A" "A" "A") ("C" "C" "C") ("T" "T") ("A") () () () ()))
+(def test-bam-mpileup-seq-ref-with-ref
+  '(() () () () () () (".") (".") ("." "." ".") ("." "." ".") ("." "." "C") ("." "." ".") ("." "." ".")
+    (".+4AGAG" ".+2GG" ".") ("." ".") ("." "." ".") ("." "." ".") (".-1G" ".+2AA" ".") ("*" ".") ("." ".")
+    ("." ".") ("." ">") (">") (">") (">") (">") (">") (">") (">" ".") (">" ".") (">" ".") (">" ".") (">" ".")
+    (">") (">+1C") ;; adjacent indel >+1T
+    (".") ("." ".") ("." ".") ("." ".") ("." ".") (".") (".") (".") (".") (".")))
 (def test-bam-mpileup-qual-ref
   '([] [] [] [] [] [] [\~] [\~] [\~ \~ \~] [\~ \~ \~] [\~ \~ \~] [\~ \~ \~] [\~ \~ \~] [\~ \~ \~]
     [\~ \~] [\~ \~ \~] [\~ \~ \~] [\~ \~ \~] [\~ \~] [\~ \~] [\~ \~] [\~ \~] [\~] [\~] [\~] [\~]
@@ -43,6 +51,58 @@
 (fact "about first-pos"
   (plp/first-pos (bam/reader test-sorted-bam-file) "ref2" 0 64) => 1)
 
+(fact
+ "about pileup-seq"
+
+ ;; ----------
+ ;; 1234567890...
+ (map
+  (fn [xs] (map #(dissoc % :end) xs))
+  (mplp/pileup-seq 1 2 [{:pos 1 :cigar "10M"}]))
+ => [[{:pos 1 :cigar "10M"}] [{:pos 1 :cigar "10M"}]]
+
+ ;;    ----------
+ ;;   ----------
+ ;;  ----------
+ ;; ----------
+ ;; 1234567890123...
+ (map
+  count
+  (mplp/pileup-seq 1 20 (map #(hash-map :pos (inc %) :cigar "10M") (range))))
+ => [1 2 3 4 5 6 7 8 9 10 10 10 10 10 10 10 10 10 10 10]
+ (map
+  count
+  (mplp/pileup-seq 101 120 (map #(hash-map :pos (inc %) :cigar "10M") (range))))
+ => [10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10 10]
+ (map
+  :pos
+  (last (mplp/pileup-seq 1 1000000 (map #(hash-map :pos (inc %) :cigar "10M") (range)))))
+ => [999991 999992 999993 999994 999995 999996 999997 999998 999999 1000000]
+
+ ;;     -----
+ ;;    ----
+ ;;   ---
+ ;;  --
+ ;; -
+ ;; 1234567890...
+ (map
+  count
+  (mplp/pileup-seq 1 10 (map #(hash-map :pos (inc %) :cigar (str (inc %) "M")) (range))))
+ => [1 1 2 2 3 3 4 4 5 5]
+
+ ;;       --------
+ ;;      ----------
+ ;;     --
+ ;;    ----
+ ;;   ------
+ ;;  --------
+ ;; ----------
+ ;; 1234567890...
+ (map
+  count
+  (mplp/pileup-seq 1 10 (map #(hash-map :pos (inc %) :cigar (str (- 10 (* (mod % 5) 2)) "M")) (range))))
+ => [1 2 3 4 5 6 6 6 6 6])
+
 (fact "about mpileup"
   (with-open [br (bam/reader test-sorted-bam-file)
               fr (fa/reader test-fa-file)]
@@ -54,7 +114,8 @@
       (map :pos mplp-ref) => (range 1 46)
       (map :seq mplp-ref) => test-bam-mpileup-seq-ref
       (map :qual mplp-ref) => test-bam-mpileup-qual-ref
-      (map :count mplp-ref2) => test-bam-pileup-ref2)
+      (map :count mplp-ref2) => test-bam-pileup-ref2
+      (map :seq mplp-ref2) => test-bam-mpileup-seq-ref2)
 
     (let [mplp-ref (doall (plp/mpileup fr br "ref"))]
       (map :rname mplp-ref) => (repeat 45 "ref")
@@ -62,7 +123,7 @@
       (apply str (map :ref mplp-ref)) => "AGCATGTTAGATAAGATAGCTGTGCTAGTAGGCAGTCAGCGCCAT"
       (map :count mplp-ref) => test-bam-pileup-ref
       (map :pos mplp-ref) => (range 1 46)
-      (map :seq mplp-ref) => test-bam-mpileup-seq-ref2
+      (map :seq mplp-ref) => test-bam-mpileup-seq-ref-with-ref
       (map :qual mplp-ref) => test-bam-mpileup-qual-ref)))
 
 (fact "mpileup region"
@@ -75,6 +136,6 @@
           (apply str (map :ref mplp-ref1)) => "AGCATGTTAGATAAGATAGCTGTGCTAGTAGGCAGTCAGC"
           (map :count mplp-ref1) => (take 40 test-bam-pileup-ref)
           (map :pos mplp-ref1) => (range 1 41)
-          (map :seq mplp-ref1) => (take 40 test-bam-mpileup-seq-ref2)
+          (map :seq mplp-ref1) => (take 40 test-bam-mpileup-seq-ref-with-ref)
           (apply str (map :ref mplp-ref2)) => "AGGTTTTATAAAACAATTAAGTCTACAGAGCAACTACGCG")))