Call javascript from asp.net page

I have 2 .net radio buttons on my page.

When the user clicks a button I want to change the contents/source of a drop down box on my page without doing the round trip to the server.

E.g.

If radio button 1 clicked then
call poDropDown1()
else
call dropdown2()
End if

Can anyone point me in the right direction ?
The dropdown must be populated from 1 or other of the .net methods.

Thanks in Advance

I think in the radio button contol, put an onclick= statement in. I haven't verified it, but that was what I read in a book somewhere. Then, if you also want server side code to execute, you would put a onserverclick= statement.

Code:

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<asp:RadioButton ID=blah onclick=poDropDown1() ; />

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With this way, you are going to point both radio buttons to the same method, and that method needs to figure out which one clicked.