There is no evident and precise data regarding the effect of cholecystokinin octapeptide (CCK-OP) on the migrating myoelectric complex (MMC) in sheep. Thus, in five rams seven bipolar platinum electrodes were implanted in the abomasal antrum and entire small intestine. The strain gauge force transducer was also attached near the duodenal electrode in three of these animals. During the experiments the myoelectric and motor activity was continuously recorded in fasted and non-fasted sheep. During the recordings two normal consecutive phases 3 of the MMC were recorded. Then, slow injections of CCK-OP of 0.02; 0.2 and 2.0 _g/kg of body weight were given intravenously during phase 1, 2a or 2b of the MMC, identified in the duodenum, until next two consecutive phases 3 MMC were recorded. The moderate dose of CCK-OP administered during phase 2a in non-fasted animals shortened the MMC cycles significantly while the highest dose of the hormone increased the cycle duration and inhibited phase 3 MMC in the duodenum. No such effect was observed in the jejunum. However, duration of phase 3 in this region was decreased mostly by the highest dose of CCK-OP. It can be concluded that CCK inhibits the MMC in ovine small bowel and its effect in the duodenum is most pronounced