<script type="text/javascript">
function change(obj)
{
var name = obj.name;
if(name != 's1')
{
var s1 = document.getElementById("s1");
for(var i = 0; i<s1.length; i++)
{
if(s1[i].value == obj.value)
{
s1[i].selected = true;
}
}
}
if(name != 's2')
{
var s2 = document.getElementById("s2");
for(var i = 0; i<s2.length; i++)
{
if(s2[i].value == obj.value)
{
s2[i].selected = true;
}
}
}
}
</script>
<select name='s1' id='s1' onchange="change(this)">
<option value="1">aaa</option>
<option value="2">bbb</option>
<option value="3">ccc</option>
</select>
<select name='s2' id='s2' onchange="change(this)">
<option value="1">aaa</option>
<option value="2">bbb</option>
<option value="3">ccc</option>
</select>