diff --git a/ProcessFASTQ.ipynb b/ProcessFASTQ.ipynb
index 3555de00cab9d4f56d6b774f3f793b75113f4be0..11758718b03b0f334e4104251194cf0bf976511b 100644
--- a/ProcessFASTQ.ipynb
+++ b/ProcessFASTQ.ipynb
@@ -751,6 +751,40 @@
     "print(\"Filtering non-codant tRNA run time : {0}\".format(delta))"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "# Testing\n",
+    "\n",
+    "with open(\"3-Filtered/\"     +fname+\".fastq\",\"r\") as filtered, \\\n",
+    "     open(\"4-Bowtied/\"      +fname+\".sam\",\"r\")   as matches,  \\\n",
+    "     open(\"5-ncRNA-Removed/\"+fname+\".fastq\",\"w\") as substracted: \n",
+    "    \n",
+    "    # Iterator over fastq file\n",
+    "    filt_iter = SeqIO.parse(filtered,\"fastq\")\n",
+    "    \n",
+    "    # Strip header (as in original script)\n",
+    "    for _ in range(415-3): matches.readline()\n",
+    "\n",
+    "    # Check last lines\n",
+    "    print(matches.readline())\n",
+    "    print(matches.readline())\n",
+    "    print(matches.readline())\n",
+    "        \n",
+    "    # Generator over fastq where the corresponding sam field is 4,\n",
+    "    # meaning no reported alignment\n",
+    "    sub_iter = (rec for rec in filt_iter \\\n",
+    "                if matches.readline().split('\\t')[1] == '4')\n",
+    "\n",
+    "    # Write back fastq\n",
+    "    SeqIO.write(sub_iter,substracted,\"fastq\")"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},