diff --git a/src/findAndReplaceDOMText.js b/src/findAndReplaceDOMText.js
index 359eef1..62f99bb 100644
--- a/src/findAndReplaceDOMText.js
+++ b/src/findAndReplaceDOMText.js
@@ -29,32 +29,51 @@ window.findAndReplaceDOMText = (function() {
    * @param {String|Element|Function} replacementNode A NodeName,
    *  Node to clone, or a function which returns a node to use
    *  as the replacement node.
+   * @param {Number} captureGroup A number specifiying which capture
+   *  group to use in the match. (optional)
    */
-  function findAndReplaceDOMText(regex, node, replacementNode) {
+  function findAndReplaceDOMText(regex, node, replacementNode, captureGroup) {
 
-    var m, index, matches = [], text = _getText(node);
+    var m, matches = [], text = _getText(node);
     var replaceFn = _genReplacer(replacementNode);
 
     if (!text) { return; }
 
     if (regex.global) {
       while (m = regex.exec(text)) {
-        if (!m[0]) throw 'findAndReplaceDOMText cannot handle zero-length matches';
-        matches.push([regex.lastIndex - m[0].length, regex.lastIndex, m]);
+        matches.push(_getMatchIndexes(m, captureGroup));
       }
     } else {
       m = text.match(regex);
-      index = text.indexOf(m[0]);
-      if (!m[0]) throw 'findAndReplaceDOMText cannot handle zero-length matches';
-      matches.push([index, index + m[0].length, m]);
+      matches.push(_getMatchIndexes(m, captureGroup));
     }
 
     if (matches.length) {
       _stepThroughMatches(node, matches, replaceFn);
     }
-
   }
 
+  /**
+   * Gets the start and end indexes of a match
+   */
+  function _getMatchIndexes(m, captureGroup) {
+
+    captureGroup = captureGroup || 0;
+ 
+    if (!m[0]) throw 'findAndReplaceDOMText cannot handle zero-length matches';
+ 
+    var index = m.index;
+
+    if (captureGroup > 0) {
+      var cg = m[captureGroup];
+      if (!cg) throw 'Invalid capture group';
+      index += m[0].indexOf(cg);
+      m[0] = cg;
+    } 
+
+    return [ index, index + m[0].length, [ m[0] ] ];
+  };
+
   /**
    * Gets aggregate text of a node without resorting
    * to broken innerText/textContent
diff --git a/test/test.js b/test/test.js
index 22bb616..3f3247b 100644
--- a/test/test.js
+++ b/test/test.js
@@ -106,4 +106,36 @@ test('Custom replacement function - correct ordering', function() {
 		return document.createTextNode(fill);
 	});
 	equal(nCalled, 3);
+});
+
+test('Capture groups', function() {
+
+	var text = 'TEST TESThello TESThello TESThello';
+	var d = document.createElement('div');
+
+	d.innerHTML = text;
+	findAndReplaceDOMText(/(TEST)hello/, d, 'x', 1);
+	htmlEqual(d.innerHTML, 'TEST <x>TEST</x>hello TESThello TESTHello');
+
+	d.innerHTML = text;
+	findAndReplaceDOMText(/(TEST)hello/g, d, 'x', 1);
+	htmlEqual(d.innerHTML, 'TEST <x>TEST</x>hello <x>TEST</x>hello <x>TEST</x>hello');
+
+	d.innerHTML = text;
+	findAndReplaceDOMText(/\s(TEST)(hello)/g, d, 'x', 2);
+	htmlEqual(d.innerHTML, 'TEST TEST<x>hello</x> TEST<x>hello</x> TEST<x>hello</x>');
+});
+
+test('Word boundaries', function() {
+
+	var text = 'a go matching at test wordat at';
+	var d = document.createElement('div');
+
+	d.innerHTML = text;
+	findAndReplaceDOMText(/\bat\b/, d, 'x');
+	htmlEqual(d.innerHTML, 'a go matching <x>at</x> test wordat at');
+
+	d.innerHTML = text;
+	findAndReplaceDOMText(/\bat\b/g, d, 'x');
+	htmlEqual(d.innerHTML, 'a go matching <x>at</x> test wordat <x>at</x>');
 });
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