Referring to your msg of 14 Jan 1997:

Hi Jeffrey.

 JH> I would like to monitor all incoming and/or outgoing data on the
 JH> serial port. Now, that wouldn't be to difficult if my program was
 JH> the only one using the com-port, but the case is that my program is
 JH> the 'third-party' and an other program is taking care of
 JH> communication.

By far the best solution is to put a datascope-like device on the COMport!
It is objective ('second opinion'), gives exact timing on port-level and it
does not disturb normal behaviour/performance of your system and
application. 
I use my laptop with 2 comports for this purpose to monitor and debug my
own multithreaded communications programs. I have written such a monitor
program myself. Not too difficult in OS/2 to listen to 2 COM-ports
simultaenously! And it was well worth the effort. I made this program for a
specific purpose (a computer controlled model railroad) I also built in an
interpretor of all commands and data for this environment, saved me a lot
of debugging time!  

Cheers, Rob 
--- timEd/2 1.10+