Thanks much Dan for the info. Looking back at by previous posts, I see that I never made it clear that the question is relative to a WebDialog associated with a plugin. Don't know if that matters but just so you know.
Eureka I have found it. It was all a matter of where the onChange was. Because the onClick was part of each radio button statement, I assumed it was the same with the select list. Instead it just needed to be in the <select> statement itself. Thanks again to one and all for the links that put me on the right path to find the answer.
def showme()
@dlg=UI;;WebDialog.new("VerySimple", true,"Test",500,300,10,10,true)
@dlg.set_html(
"<html>
<body>
<form>
<select onChange='tellSketchup(value)'>
<option value='option1' >Option 1</option>
<option value='option2' >Option 2</option>
</select> ; Head Type<br><br>
</form>
<script type='text/javascript'>
function tellSketchup(value)
{
window.location='skp;OptionChanged@'+value;
}
</script>
</body>
</html>"
)
@dlg.show {} #show it
@dlg.add_action_callback("OptionChanged") {|d,p|
puts "OptionChanged value=#{p}"
}
end