Many biomedical experiments require a precisely timed real-time (RT) computer interface. Because commonly used desktop operating systems are inherently non-real-time, real-time laboratory computer systems are often based on outdated DOS software or expensive proprietary real-time operating systems. Here we discuss a real-time computing system, based on the free RT-Linux operating system, which we have developed for adaptive pacing control in a clinical cardiac electrophysiology laboratory. This powerful, flexible, and inexpensive system demonstrates that RT-Linux is well suited for real-time biomedical experiment interface.