There are Many solutions for your problem and one of the easy solution is to put your list box in an update panel and when ever u click in list box then the the Update panel will be updated and you will get the new date into your Update panel.
If you need details solution then please post your complete requirement, what u want to do after selecting the Items in the List box and further details. If you seriously concerned about the Performance then I prefer you to Go with Ajax Network call which result in very Least Data Transfer Between Client and the Server and one more best approach for this Using jQuery Ajax its very light weight Ajax Library with lots of features. *Happy Coding* -- N i t i :- The future belongs to those who believe in the beauty of their dreams...
