1. The effects of verapamil on dopamine-, secretin- and pancreozymin-induced pancreatic secretion were investigated in the isolated, blood-perfused canine pancreas in vivo. 2. The volume of pancreatic secretion either in the resting state or induced by pancreozymin given intra-arterially (i.a.) was decreased by an infusion of 5 micrograms/min of verapamil; that induced by dopamine or secretin i.a. was also decreased but the changes were not statistically significant. 3. Protein concentration in pancreatic juice either in the resting state or in that of stimulated secretion by pancreozymin was decreased significantly, but protein concentration induced by dopamine or secretin was not affected, by verapamil treatment. 4. Verapamil had no effect on bicarbonate concentration in pancreatic juice secreted either in the resting state or when stimulated by these secretagogues.5. These results suggest that verapamil, at least in part, may affect the secretory mechanisms of acinar cells but not that of the ductular cells.