function VerificaSeleccionComboDoctores() {
    if ( 0 == document.comboDoctores.ciudad.selectedIndex ) {
        alert("Por favor seleccione una Ciudad.");
        return false;
    }
    else  return true;
}
function EscribeComboDoctores( url_base ) {
	<!-- Genera el combo de ciudades para buscar doctores -->
	html = '';
	html = html + 'BUSQUE UN DOCTOR ESPECIALISTA EN THERMAGE\n';
	html = html + '<form action="' + url_base + 'doctores.asp" method="post" name="comboDoctores" id="comboDoctores" onsubmit="return VerificaSeleccionComboDoctores();">\n';
	html = html + '<select name="ciudad">\n';
	html = html + '<option value="">Seleccione una Ciudad&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</option>\n';

	html = html + '<option value="1">Canc&#250;n, Q.Roo.</option>\n';

	html = html + '<option value="4">Ciudad Juarez, Chih.</option>\n';

	html = html + '<option value="18">Culiac&#225;n, Sin.</option>\n';

	html = html + '<option value="5">Guadalajara, Jal.</option>\n';

	html = html + '<option value="19">Irapuato, Gto.</option>\n';

	html = html + '<option value="6">Le&#243;n, Gto.</option>\n';

	html = html + '<option value="7">Mazatl&#225;n, Sin.</option>\n';

	html = html + '<option value="8">M&#233;rida, Yuc.</option>\n';

	html = html + '<option value="9">M&#233;xico, D.F.</option>\n';

	html = html + '<option value="10">Monterrey, N.L.</option>\n';

	html = html + '<option value="20">Morelia, Mich.</option>\n';

	html = html + '<option value="11">Puebla, Pue.</option>\n';

	html = html + '<option value="12">Reynosa, Tamps.</option>\n';

	html = html + '<option value="13">Tijuana, B.C.</option>\n';

	html = html + '<option value="14">Torre&#243;n, Coah.</option>\n';

	html = html + '<option value="15">Uruapan, Mich.</option>\n';

	html = html + '<option value="16">Xalapa, Ver.</option>\n';
	
	html = html + '</select>\n';
	html = html + '<input type="image" name="go" src="' + url_base + 'shared/locator_go.gif" width="44" height="16" border="0" /><br />\n';
	html = html + '</form>	\n';	
	
	document.write(html);
}