The effect of intravenous infusion of synthetic motilin on gastric motor activity was investigated by means of chronically implanted force transducers in 4 conscious dogs. Since the gastric motor pattern consisted of two major subpatterns, digestive and interdigestive motor activity, motilin was tested for its motor stimulating activity in both states. It was found that motilin had no influence upon gastric motor activity in the digestive state. However, during the interdigestive state, intravenous infusion of motilin in doses of 0.3-2.7 microgram/kg/hr induced motor activity similar to the naturally occurring interdigestive contractions in a dose-related fashion. Since motilin is released by duodenal alkalinization in the dog, it may be postulated that motilin is a substance to control the interdigestive contractions in the dog, although other reports describe motilin release by duodenal acidification and inhibition of gastric emptying in man. Endogenous stimuli leading to motilin release may be different among species. The present study clearly indicates that motilin induces a contractile pattern similar to that seen during the interdigestive state in conscious dogs.