Acetylcholine (ACh), dopamine, and dibutyryl-adenosine 3',5'-monophosphate (dbcAMP) were applied iontophoretically to the rabbit superior cervical ganglion cells from triple-barreled micropipettes, and the response was recorded by intracellular techniques. All ganglion cells tested responded to the depolarizing action of ACh, whereas less than half of the cells that responded to ACh were hyperpolarized by dopamine. This effect was blocked by low concentrations of haloperidol. None of the cells examined responded to dbcAMP applied by iontophoresis. Hence, the present result is not consistent with the concept that a cyclic AMP mechanism underlies the hyperpolarizing effect of dopamine.