The objective was to determine whether motilin regulates cyclical interdigestive motility in the jejunum as well as in the duodenum. In four conscious dogs with an intact innervated duodenum, an autotransplanted (extrinsically denervated) 75-cm loop of proximal jejunum, and an autotransplanted, in situ distal jejunum, interdigestive myoelectrical complexes cycled independently in all three regions of small bowel. Plasma concentration of motilin was greater during phase III of the duodenal cycles (304 +/- 37 pg/ml) than during phase I (235 +/- 37 pg/ml) or phase II (235 +/- 39 pg/ml; P less than 0.05), but the concentration did not vary consistently with the phases of the cycles in the autotransplanted jejunal segments. Intravenous infusions of motilin (0.6 microgram/kg/min for 5 hr), begun 15-30 min after passage of phase III through the duodenum, shortened the interval between phase IIIs in the duodenum from 147 +/- 14 min before infusions to 44 +/- 3 min during the infusions (P less than 0.05), but did not alter consistently the interval between phase IIIs in the autotransplanted jejunal segments. Feeding decreased plasma motilin concentration. The data were consistent with motilin regulation of interdigestive motility in intact, innervated canine duodenum but not in extrinsically denervated jejunum.