The inhibitory effect of intravenous infusion of secretin (0.05 CU kg-1h-1) and somatostatin (60 pmol kg-1h-1), given alone or in combination, on pentagastrin-stimulated (100 ng kg-1 h-1) acid secretion was studied in 10 healthy subjects. Secretin inhibited acid secretion by 54% (p less than 0.05), and somatostatin inhibited by 70% (p less than 0.05). The combined infusion of secretin and somatostatin decreased acid output by 64% (p less than 0.05). The differences between the three groups were not significant (p greater than 0.05). Median plasma concentrations of secretin and somatostatin were of the same magnitude as seen after duodenal acidification. The present study did not demonstrate any interaction between secretin and somatostatin in the inhibition of gastric acid secretion.