Interdigestive contractile activity of the gallbladder, the stomach, and the duodenum was measured by means of chronically implanted force transducers in five conscious dogs. During the interdigestive state, contractions of the gallbladder were identified to be closely associated with the initial period of phase II of the interdigestive migrating contractions (IMC) in the duodenum. The mean contractile force of the gallbladder during this phase was 6.5 +/- 0.77 g, which corresponded to approximately 80% of the force of the postprandial contractions. When the duodenum exhibited phase II contractions, the gallbladder had already returned to the resting level. Intravenous infusion of synthetic motilin induced IMC in the stomach and duodenum and during the initial period of motor response of the duodenum reproduced contractions in the gallbladder that were identical to the natural contractions as to their period and pattern. We cannot yet ascribe the interdigestive contractions observed in the gallbladder to the direct action of motilin, but the present study clearly indicates that the gallbladder contracts even in the interdigestive state, and the contractions are associated with the phase II contractions in the duodenum.