A system designed to evaluate ventilatory responses to hypercapnia and hypoxia is described. Parameters measured include minute ventilation (VE), breathing rate (f), tidal volume (VT), inspiratory time (TI), fractional inspiratory time (TI/TTOT), mean inspiratory flow (VT/TI), mouth occlusion pressure (P100), and either end tidal partial pressure of carbon dioxide (PETCO2). or end tidal partial pressure of oxygen (PETO2). The system allows rapid reproducible measurement of total ventilatory output, neuromuscular force generated, drive and timing parameters of respiratory control for use in the clinical assessment of patients with pulmonary, neurologic or non-thoracic disease. The system's architecture was based primarily on currently available microcomputer components designed for the IEEE 696 bus.