Thanks, Joel. But I have to write my own program, though I know there are already commercial products available. This is one of my work assignments. Sally:)

Hi, Could someone advise me how to spy at a com port when another existing running application is using the same com port for serial communication? Preferably with sample coding. My intention is to build a serial port monitor Because, it would complain error...com port in use, then my spy program will exit. I use CreateFile Function. thanks, Sally:)