>I think I was not clear in my question. I don't want post back itself to happen based on the Part Number field. i.e., If the Part Number is empty, I want postback on Unit Price field and if the Part Number is not empty, I want postback on Quanity field.
>
>Conditional AutoPostBack?

I don't know if you can control which fields are sent as part of the postback and which ones not. For me, I leave that as is and handle it on the server side.