Doxapram was administered to 50 spontaneously breathing patients receiving enflurane and nitrous oxide for surgical anesthesia. A similar group acted as control. Significant depression of ventilation did not occur in the control group of patients, nor did doxapram produce a reduction of end tidal CO2 concentrations. It is suggested that surgical stimulation and concomitant nitrous oxide administration reduced the ventilatory depressant effect of enflurane and that the effect of doxapram was attenuated by the actions of enflurane on the peripheral chemoreceptors.