To investigate the hypothesis that the impaired respiratory drive noted in morbid obesity was attributable to altered dopaminergic mechanisms acting on peripheral and/or central chemoreflex sensitivity, seven obese and seven lean Zucker rats were studied at 11 wk of age. Ventilation (E) was measured by the barometric technique during hyperoxic (100% O₂), normoxic (21% O₂), hypoxic (10% O₂), and hypercapnic (7% CO₂) exposures after the administration of vehicle (control), haloperidol [Hal, 1 mg/kg, a central and peripheral dopamine (Da) receptor antagonist], or domperidone (Dom, 0.5 mg/kg, a peripheral Da receptor antagonist). In both lean and obese rats, Hal increased tidal volume and decreased respiratory frequency during hyperoxia or normoxia, resulting in an unchanged E. In contrast, Dom did not affect tidal volume, frequency, or E during hyperoxia or normoxia. During hypoxia, however, E significantly increased from 1,132 ± 136 to 1,348 ± 98 ml · kg¹ · min¹ (P < 0.01) after the administration of Dom in obese rats, whereas no change was observed in lean rats. Hal significantly decreased E during hypoxia compared with control in lean but not obese rats. In both lean and obese rats, Hal decreased E in response to hypercapnia, whereas Dom had no effect. Our major findings suggest that peripheral chemosensitivity to hypoxia in obese Zucker rats is reduced as a result of an increased dopaminergic receptor modulation in the carotid body.