Refreshing dropdown based on selection

Hi guys,

               Though iam working in asp.net from 3 years iam new to asp.I need to work on this app and make some changes.I have a dropdown which i need to fill values on page load.When the user selects the value from first dropdown i need to populate second dropdown by passing  id of first dropdown and get values from database.I need to make changes in onchange event in first dropdown.How can i do it can someone provide me a sample code for it i know it would be pretty simple but am unable to do it.

Can some one let me know how to call stored procedures from asp pages. 

Thanks for looking through my post.
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