Benzquinamide, an ataractic antiemetic, is also a respiratory stimulant of modest efficacy. In a dose of 0.7 mg/kg intravenously it increases ventilation at constant controlled alveolar CO2tension by 12.4 1/min. The curve of the ventilatory response to CO2after 0.7 to 1.4 mg/kg is parallel to and 10 torr to the left of the pre-drug response curve. Prochlorperazine, a phenothiazine antiemetic studied in comparison, has little respiratory effect in doses of 0.35 mg/kg or less except as associated with akathisic arousal. After stable morphine-induced respiratory depression, benzquinamide (0.7 mg/kg) gave brief stimulation and little change in ventilation for 3 hours thereafter. Prochlorperczine (0.18 mg/kg), by contrast, potentiated the opioid depression, with some suggestion of waning effect by 3½ hours.