The effect of chronic administration of bethanechol and pentagastrin on the pancreas was examined. Rats were either antrectomized or subjected to a sham operation. Three weeks after surgery, rats received a daily intraperitoneal injection of either bethanechol (12 mg/kg) or pentagastrin (250 micrograms/kg) for 14 days. The fasting serum gastrin after bethanechol treatment increased to 1.89 times that of controls treated with saline. Although antrectomy decreased fasting serum gastrin to approximately 40% of controls, serum gastrin increased by 2.17 times that of the antrectomized rats and 1.37 times that of controls in the bethanechol group. After 14 days of bethanechol treatment, weight and amylase in the pancreas increased significantly compared with control; DNA and protein also increased 1.3 and 1.5 times that of control. The increase in DNA and pancreatic weight indicated that hyperplasia was the predominant mechanism. The pancreas showed atrophy in antrectomized rats but this was reversed by both bethanechol and pentagastrin. The results indicate that either endogenous gastric or extragastric gastrin release by cholinergic stimuli may have an important role in the regulation of pancreatic growth.