The effect of the new antiulcer agent plaunotol on the release of endogenous secretin and the pancreatic exocrine secretion was investigated in anesthetized rats. In 48 rats with pancreatic and biliary diversion, continuous intraduodenal infusion of plaunotol in 3 graded doses (5, 20 and 80 mg/h/rat) resulted in significant increases in both circulating plasma secretin concentration and pancreatic exocrine secretion, including volume and bicarbonate output, in a dose-dependent manner (r = 0.655, p less than 0.001; r = 0.598, p less than 0.001; r = 0.436, p less than 0.01, respectively). The pancreatic bicarbonate output was closely correlated to plasma secretin concentrations (r = 0.631, p less than 0.001). Amylase output also increased after plaunotol administration, but not in a dose-dependent manner (r = 0.092, n.s.). These findings suggest strongly that the increase in pancreatic secretion of fluid and bicarbonate output was mainly due to increased endogenous secretin release resulting from plaunotol administration.