>thanks Alex. Is there a preferred test for its existence?

That I don't know as I'm not a .Net guru.

I would think that a check in some registry key would do it. OTOH your .Net program (Exe) simply will not run if the framework is not installed. The installer or install routine you use to deliver your program is suppossed to check beforehand and install (or download/install) the framework if not already there.