AbstractTwo large multiple transmitter neurons are located in each buccal ganglion ofTritonia. One of these neurons (B11) contains large quantities of two neuropeptides and acetylcholine (ACh), whereas the other neuron (B12) appears to contain the same two peptides but no ACh. One of the peptides present in these neurons has recently been sequenced and is termed small cardioactive peptide B (SCPB). Both neurons regulate the motility of the gut. Stimulation of B11 produces a posteriorly directed peristalsis after a short latency. This gut movement may normally accompany swallowing. B11 stimulation also produces an increase in the rate of endogenous contractile activity that is similar to that produced by superfusion of the gut with low concentrations (10−8M) of SCPB. Stimulation of B12 produces a vigorous longitudinal contraction of the gut, initiated in the posterior part of the gut and not peristaltic in nature. This movement appears incompatible with swallowing behavior and may be involved in regurgitatio