Hola
corona
Prueba este ejemplo:
Código PHP:
<html>
<head>
<script type="text/javascript">
function cambiar(obj) {
sel = obj.form.getElementsByTagName('select');
for (i=0; ele = sel[i]; i++)
if (ele != obj)
ele.selectedIndex = 0;
}
</script>
</head>
<body>
<form>
<select onchange="cambiar(this)">
<option>---</option>
<option>uno</option>
<option>dos</option>
</select>
<select onchange="cambiar(this)">
<option>---</option>
<option>uno</option>
<option>dos</option>
</select>
</form>
</body>
</html>
Saludos,
