ASP.NET Validation

I have a webform that holds several TextBox Controls, RequiredFieldValidators and a button. When I click the button the form is validated and if it is invalid a message box pops up. My question however: is there a way to execute code, after the button click event but before the message box pops up, as I try to hide controls after the button is clicked even if the input is invalid and the message box pops up Hope u see what I mean thx Gash