Binding dropdownlist

Question

I want to stop binding dropdownlist again and again after postback.

 

For eg. I already bind 3 datas into dropdown list. After I choose one in drop down list and click one button called search , it will show the data of selected but now the drop down list is with 6 data. after click again , there are 9, 12 again and again.

 

Can anyone help me to stop binding dropdownlist.

 

Thanks a lot :-)