Five male volunteers performed 20 min of steady-state submaximal exercise on a motor-driven treadmill at five intensities (30, 45, 60, 75, and 90% VO2 max) as well as several maximal aerobic capacity tests. Peripheral venous plasma testosterone concentrations increased above resting values in proportion to exercise intensity. However, this increase in plasma testosterone concentration was virtually equal in magnitude to the decrease in plasma volume observed consequent to the exercise bouts, resulting in no change in total testosterone contents. There was an unexpected anticipatory elevation in resting preexercise control testosterone concentration and content with increasing work intensity. The possibility that testosterone has a direct role in the organism's response to whole-body exercise is questioned.