high speed collision detection

[Billystyx]

Hello - I have had a look through the forum and can't seem to find any answers on this (a few questions though).
I am trying to get a collision detection between balls moving at different speeds across the stage. I am (currently) using hitTest, but the problem is that the speed of the moving balls varies, and obviously if the speed increment takes one ball 'over' another, then the hitTest is missed. At slower speeds it works fine.
Is there a way around this?