My html:

 <script type="text/javascript">

    $(function() {

        $("#bt1").click(function() {

            var f = $("#form1");
            var formData = f.serialize();

            alert(formData);
        });

    }); 
</script> 

 <div id="div1">
      <form id="form1" action="/Home/Test1" method="post" name="down">
        <div id="div2">
            <input id="input1" type="text" value="2" />
        </div>    
      </form>
  </div>

 <input type="submit" id="bt1" />

When I fire up the click event, formData is empty. I'm using jQuery 1.4.2.