Problem with AJAX

Hai All,

I got one problem in ajax.im applying ajax for 3 dropdown lists when im selecting 3 dropdown values in first time it is working, in 2nd time it is taking the request as postback for same values(previously selected values) and notpostback for other values(newly selected values).If i want to select same values for 2nd or 3rd time what i have to do..?plz any one help me………

Thanks,
Aswath.