The effect of cisplatin on interdigestive myoelectric activity (IDMA) of the gastric antrum, duodenum and jejunum, plasma concentration of motilin, and animal behavior was studied in seven conscious dogs with gastric cannulas and platinum electrodes implanted on the serosal surface of antrum and upper small intestine. Cisplatin given intravenously in a dose of 2 mg/kg resulted in complete interruption of IDMA and produced predominantly phase II-like activity, lasting as long as 24 hr. Six of the seven dogs exhibited retropropagation of spike bursts from the jejunum to the antrum which was accompanied by emesis. Retropropagation of spike bursts did not occur in one dog who did not exhibit emesis. In addition, abnormal spike bursts occurred frequently, including simultaneously occurring spike bursts in both duodenum and jejunum and nonpropagating short spike bursts in isolated segments of the upper small intestine. As phase III of IDMA disappeared, plasma motilin concentrations remained comparable to those in phase II of normal IDMA but without the cyclic increases. These studies indicate that cisplatin interrupts the regular cycle of IDMA as well as the plasma motilin cycle and produces retropropagation of spike bursts and abnormal spike bursts. These changes in both motility and plasma motilin levels may play a part in the mechanism of emesis induced by cisplatin in dogs.