Hi Jim There are several things that can couse problems. It might be that you are being too fast, not too slow. Most of the newer serial chips hold a larger buffer. Several characters may be buffered up in the chip. You need to make sure that the character has been sent and that you've waited for enough delay time for your other machine to respond before sending another character to the serial chip. You can't just handshake on the status lines from the serial chip. You may have to look at the time chip for timing information. Also, I assume you are using the system calls. If not, you may have issues if your running under windows or in a DOS box under windows because windows thinks it owns the serial and will periodically steal characters from the input. There is a way to remove a serial port from windows but I've never tried it for this particular problem. Dwight