This simple scripts show a possibility to call a JavaScript function that retrieves a variable passed from drop down box as a parameter and then the JavaScript redirects the browser to the variable that was passed to it.

Redirect with a Dropdown Menu in JavaScript

<script type="text/javascript">
function do_redirect(site){
   window.location.href = site;
}
</script>
 
<select onchange="do_redirect(this.value)">
   <option value="#">What site would you like to see?</option>
   <option value="http://www.google.com">Google</option>
   <option value="http://www.yahoo.com">Yahoo</option>
   <option value="http://www.apphp.com">ApPHP</option>
</select>