AbstractThe buccal ganglia of the snail,Helisoma trivolvis, contain an intrinsic system of dopamine‐containing neurons (Trimble, Barker, and Bullard, 1983). Dopamine, when bath applied to the isolated buccal ganglia, activates patterned motor output in a dose‐dependent fashion. Haloperidol blocks the activating effect of dopamine, but the similar activation evoked by serotonin is not blocked by haloperidol. We suggest that there are two separate mechanisms for activating patterned motor output from the buccal ganglia. One is serotonergic, emanating from identified cerebral ganglion cells (Granzow and Kater, 1977), while the other is dopaminergic, involving neurons intrinsic to the buccal gang