Hola
emont
Prueba esto:
Código PHP:
<html>
<head>
<script type="text/javascript">
function validar(frm) {
obj = frm.sel.options[frm.sel.selectedIndex];
alert(obj.parentNode.label);
}
</script>
</head>
<body>
<form>
<select name="sel">
<optgroup label="Categoria 1">
<option>Subcategoria 1</option>
<option>Subcategoria 2</option>
</optgroup>
<optgroup label="Categoria 2">
<option>Subcategoria 1</option>
<option>Subcategoria 2</option>
</optgroup>
</select>
<input type="button" onclick = "validar(this.form)" />
</form>
</body>
</html>
Saludos,
