The effect of dopamine on the ventilatory response to transient asphyxia was examined to test the hypothesis that dopaminergic mechanisms modulate carotid body function in humans and to determine whether a change in ventilatory responsiveness is effected by changes in tidal volume or breathing frequency. Five healthy adults were subjected to brief episodes of hypercapnic hypoxia before and at the end of a 45-min intravenous infusion of dopamine hydrochloride (5 micrograms/kg/min). Mean ventilatory response to hypercapnic hypoxia decreased from 1.71 +/- 0.33 L/min/% SaO2 (+/- SD) to 1.30 +/- 0.28 L/min/% SaO2 (p less than 0.05) during dopamine infusion. The fall in ventilatory response was due to a fall in the frequency of breathing (p less than 0.01). Dopamine infusion also produced a small decrease in resting minute ventilation (p less than 0.05) and a small increase in resting end-tidal PCO2 (p less than 0.05). No change was noted in the ventilatory response to progressive hypercapnia. These findings suggest that dopamine acts at the carotid body to depress its response to transient hypoxic stimulation and that this effect is to selectively slow the rate of breathing.