Gastric motility and plasma gastrin concentration have been measured in 6 healthy volunteers before and after stepwise gastric distention. Distention was performed by filling a flaccid thin-walled bag, which was connected with a low pressure transducer for measuring intragastric pressure variations. Stepwise increase in gastric volume from 0-600 ml caused graded increases in gastric motility. No significant change was seen in the plasma gastrin level. When gastric distention was performed concomitantly with constant infusion of somatostatin (0.05 mg/h and 0.50 mg/h) in the same individuals on different days, motility was significantly reduced, without any changes in the plasma gastrin concentration. It is concluded that somatostatin, which probably plays a role in the gastro-intestinal tract, may have a physiological effect in the regulation of gastric motility too. This motility effect of somatostatin seems to be independent of any effect on the gastrin concentration.