try this solution:
PHP Code:
<script type="text/javascript">
var xmlHttp;
function addPubNum( id, name, pubnum ) {
document.forms['addpub'].elements[ pubnum ][ document.forms['addpub'].elements[ pubnum].length ] = new Option( name, id )
}
function remPubNum( pubnum ) {
while( document.forms['addpub'].elements[ pubnum ].length > 0 ) document.forms['addpub'].elements[ pubnum ][0] = null
}
function showPubNum(pubnum,countyid){
xmlHttp=GetXmlHttpObject();
if (xmlHttp==null) {
alert ("Browser does not support HTTP Request");
return;
}
var span_select = document.getElementById("pubnum");
var url="ajax.php?";
//url=url+"?pubnum="+pubnum
url=url+"countyid="+countyid;
url=url+"&sid="+Math.random();
xmlHttp.onreadystatechange=stateChangedPubNum('span_select');
xmlHttp.open("GET",url,true);
xmlHttp.send(null);
}
function stateChangedPubNum('span_select') {
if (xmlHttp.readyState==4 || xmlHttp.readyState=="complete") {
//eval( xmlHttp.responseText );
document.getElementById("span_select").innerHTML= xmlHttp.responseText ;
}
}
function GetXmlHttpObject(){
var xmlHttp=null;
try
{
// Firefox, Opera 8.0+, Safari
xmlHttp=new XMLHttpRequest();
}
catch (e)
{
//Internet Explorer
try
{
xmlHttp=new ActiveXObject("Msxml2.XMLHTTP");
}
catch (e)
{
xmlHttp=new ActiveXObject("Microsoft.XMLHTTP");
}
}
return xmlHttp;
}
</script>
</head>
<body>
<select name="countyid" onChange="showPubNum('span_pubid1',this.value);">
<option value="">Select County</option>
<option value="1">Antrim</option>
<option value="2">Armagh</option>
<option value="3">Carlow</option>
<option value="4">Cavan</option>
<option value="5">Clare</option>
<option value="6">Cork</option>
<option value="7">Derry</option>
<option value="8">Donegal</option>
<option value="9">Down</option>
<option value="10">Dublin</option>
<option value="11">Fermanagh</option>
<option value="12">Galway</option>
<option value="13">Kerry</option>
<option value="14">Kildare</option>
<option value="15">Kilkenny</option>
<option value="16">Laois</option>
<option value="17">Leitrim</option>
<option value="18">Limerick</option>
<option value="19">Longford</option>
<option value="20">Louth</option>
<option value="21">Mayo</option>
<option value="22">Meath</option>
<option value="23">Monaghan</option>
<option value="24">Offaly</option>
<option value="25">Roscommon</option>
<option value="26">Sligo</option>
<option value="27">Tipperary</option>
<option value="28">Tyrone</option>
<option value="29">Waterford</option>
<option value="30">Westmeath</option>
<option value="31">Wexford</option>
<option value="32">Wicklow</option>
</select>
<span id="span_pubid1"><select name="pubid1" disabled="disabled"><option value=""></option></select></span>
<input type="submit" value="Add">