Determine if Invoke is Required

How can I determine if an invoke is required? I have a method that needs to display a dialog. The problem is that this method could be called from anywhere in the application from any thread. So I want to put a check in the method to see if I should use Invoke to display the dialog or if I can just display it directly.

[327 byte] By [BaltimoreJohna] at [2007-10-2 23:46:03]