Show/Hide controls very slow.

Hi,
Would like to seek advice, what is the best way to show/hide controls in .net?
I have a page with many show/hide depending on the control value.
eg. radio button list rbl (dynamically generated from the database values)
based on the radio button list value,will need to show/hide the other controls.
if the value is 1, will need to show or hide dropdownlist1.
if the value is 2, will need to show or hide dropdownlist2.
I tried using the javascript with rbl.Attributes.Add("onChange","return toggleDropdown();")
then in my javascript function i will show/hide the control.
However when I toggle the dropdown for the second time, it became very slow. The first time is okay.
I have also tried using ScriptManager and UpdatePanel (putting the controls inside the UpdatePanel), but it is also very slow when toggling dropdown for the second time onwards, causing the page to hang.

Any idea how to solve ...