A mechanical breathing simulator has been developed to reproduce the human breathing patterns of 0, 208, 415, 622, 830, and 1107 kg-m/min work rates. The patterns are produced by the stroke action of twin pistons controlled by interchangeable cams. Cam rotation is governed by a solid-state variable-speed and torque motor control. The breathing patterns were determined by using the voltage output from a pressure transducer. Minute volumes for the six work rates were 14.0, 20.6, 29.8, 36.7, 53.3, and 71.4 liters/min, respectively. Their corresponding maximum inspiratory flow rates were 66, 70, 94, 114, 152, and 185 liters/min.