Untitled

<html>

<head>

<script src="plugins/jquery.chained.js" type="text/javascript" charset="utf-8"></script>
<script src="plugins/jquery_states.js" type="text/javascript" charset="utf-8"></script>
<script src="plugins/jquery.js" type="text/javascript" charset="utf-8"></script>

</head>

<body>


<select id="mark">
  <option value="">--</option>
  <option value="bmw">BMW</option>
  <option value="audi">Audi</option>
</select>
<select id="series">
  <option value="">--</option>
  <option value="series-3" class="bmw">3 series</option>
  <option value="series-5" class="bmw">5 series</option>
  <option value="series-6" class="bmw">6 series</option>
  <option value="a3" class="audi">A3</option>
  <option value="a4" class="audi">A4</option>
  <option value="a5" class="audi">A5</option>
</select>


</body>


</html>


/* Koden till jquery_states.js */

$(function(){
     $("#series").chained("#mark"); /* or $("#series").chainedTo("#mark"); */
});