In order to do this, you will have to inject code into the client side
to bring up the messagebox in JavaScript. The code that is run in ASP.NET
pages is on the server side, and you definitely don't want to bring up a
message box there.

Use the Alert function in JaveScript like:

Alert("Hello");


>Using C#.
>
>How can I display a messagebox and return a value in a webform?
>
>Thanks,
>
>Jerryt