This study presents evidence that dopaminergic neurons innervate the cat carotid body. Immunocytochemical studies revealed many tyrosine hydroxylase (TH)-positive nerve fibers in the carotid body which establish extensive contacts with type I cells. All TH-positive intralobular profiles disappeared with chronic carotid sinus nerve (CSN) section, but survived sympathectomy following removal of the superior cervical ganglion. The level of endogenous dopamine (DA) in the CSN was higher than that for norepinephrine (NE). While both catecholamines were synthesized by the nerve at similar rates, NE synthesis was abolished by chronic sympathectomy, but DA synthesis remained largely unchanged following this procedure. Our data indicate that DA is not present in the CSN as a mere precursor of NE. Following a 3-hour incubation of carotid bodies with their attached nerves in media containing 20 µM³H-tyrosine, electrical stimulation of CSN C-fibers in chronically sympathectomized preparations provoked the release of ³H-DA, but not ³H-NE.