A short-duration cycle ergometer exercise test has been developed that allows four parameters of aerobic function to be discerned. These are the maximum O2 uptake, anaerobic threshold, work efficiency, and the time constant for O2 uptake kinetics. The test form is a ramp of 4-8 min duration to the limit of tolerance. The parameters determined from the ramp faithfully reproduced those obtained from several standard procedures. We conclude that a profile of aerobic function in man can be obtained from a single short-duration ramp test.