autocomplete combobox

autocomplete combobox

I tested the jQuery UI AutoComplete Combobox Demo, and I was wondering if it's possible to use the onchange event with the select html item, in the case of having cascading dropdowns.
I tried the following:

<select id="select1" onchange="javascript:PopulateValues();">
 
This didn't work out as expected. Please advise.
 
Thank you.