The effects of different doses of somatostatin (36, 180, 360 pmol/kg/h) on the motor patterns of the duodenum and on gallbladder volume in the postprandial period were evaluated. Gallbladder volume and small intestinal motor activity were monitored simultaneously in 9 normal subjects. Gallbladder volume was measured every 5 min throughout the study by real-time ultrasonography while intestinal motility was recorded manometrically by means of a low-compliance pneumohydraulic system. On day 1, the response of the gallbladder to a 972-kcal test meal was evaluated ultrasonographically to assure a normal response. On day 2, at least 2 consecutive phase III complexes of the interdigestive motor cycle were recorded. Gallbladder volume varied cyclically during the interdigestive motor cycle, with the minimum value late in phase II and the maximum early in phase I (p less than 0.01); the test meal was then administered. Following the induction of a typical pattern of postprandial motility, somatostatin infusion was started and continued for 150 min. Somatostatin, at the 180- and 360-pmol/kg/h doses, interrupted the fed pattern and induced consecutive bursts of propagated clustered activity. The characteristics of these somatostatin-induced motor patterns were similar to the spontaneous phase III of the interdigestive motor cycle. An initial reduction in gallbladder volume cycle. An initial reduction in gallbladder volume followed the ingestion of the meal; during somatostatin infusion, gallbladder volume increased to values greater than fasting values and varied cyclically with minimum values before the second episode of propagated clustered activity. These results show that somatostatin interrupts the fed pattern and elicits consecutive clusters of propagated motor activity in the duodenum that are coordinated with cyclic fluctuations in gallbladder volume.