Mark,

I agree with Jim when he says "If it isn't resetting the Input property, it is an ActiveX problem. It's been in use too many years by too many developers - I doubt that is the case here."

FWIW, I use MSCOMM to parse the serial input coming from a console used to switch video cameras as well as zooming in/out, panning left/right or tilting up/down, and, eventhough the parsing process is not trivial (is not very complicated also, but it uses regular expressions to try to understand which command(s) was(ere) sent) and the input can be somewhat fast (when zooming, panning or tilting the cameras there are several commands per second, around 15) I have experienced no problem like what you mention, but also, unfortunately, can not see what might be wrong with your code. Do you have a timer? Something I did with my code is to assign the .pcLastReading property (I called it .Buffer) to a local variable at the beginning of my process, and clearing it inmediately (afterwards I assign the "leftovers" of my process back to it) to handle the situation where the COMM event is fired while I am doing the process of the previous one.