>What I need to know is will each call to the Fn run separately if input comes in from both com ports simultaneously?? Or will the secondary function get mixed up as to which variable value to use??
>

Nope... a VFP program only has ONE thread... so, whichever port's data is noticed first will be processed, then your polling routine will see data in the ther port and deal with that.

The COM ports data should be cached... so, you shouldn't loose data from com1 if you are processing data from com2.

BOb