Myoelectric activity in various portions of the stomach and duodenum in normal and after vagotomy and intravenous injection of serotonin adipinate was studied in acute experiments on cats. Vagotomy disturbed coordination of myoelectric activity in the stomach and duodenum. Intravenous injection of serotonin adipinate restored coordination and increased myoelectric activity in the stomach, particularly, in the pylorus. Under these conditions the pacemaker of myoelectric activity in the gastric corpus and autonomic regulation of the duodenum were preserved. Intravenous injection of serotonin adipinate most significantly changed myoelectric activity in the pylorus. Myoelectric activity in the cardia increased after vagotomy against the background of serotonin adipinate. Our findings suggest that serotoninergic structures maintain functional heterogeneity of digestive organs and coordinate their interrelationships.