Carotid body chemosensitivity is modulated by the neurotransmitter dopamine. Because droperidol has potent dopamine receptor blocking capability, we studied its effects on hypoxic ventilatory response. Droperidol (2.5 mg) was administered intravenously to four volunteers and their hypoxic drive was assessed by a sudden decrease in end-tidal O2 from 106 to 53 torr. End-tidal CO2 was held constant at 41 torr throughout all experiments. Droperidol caused an increase in the slope of the hypoxia-induced ventilatory response from 0.98 +/- 0.23 to 1.87 +/- 0.31 L/min per 1% decrease in saturation (mean +/- SEM, P less than 0.05). A dopamine infusion (3 micrograms X kg-1 X min-1), which depressed hypoxic drive before the administration of droperidol, did not depress the hypoxic drive after droperidol. Droperidol potentiates the hypoxic ventilatory response, presumably by blocking the action of endogenously released dopamine.