Thanks everyone for your help. It looks like a too-hard in VC++. The solution looks to be one of the programs around that redirect the com port to an IP address, or use a cable splitter. Jim

Using visual C++, can I monitor data on a serial port opened by another application? I have an application that recieves data from a comm port. I want to write a program to idependently monitor the data that is recieved on this port, and (depending on the data) write it to a file. I don't have source to the application. Is it possible to transparently view the data on a comm port like this? I've tried using CreateFile() to get access to the port, but I get a "port in use" error. Any help appreciated. Thanks Jim