Myoelectric activity was recorded from the gastric antrum and small intestine of conscious, unrestrained guinea pigs using bipolar Ag-Ag chloride electrodes that had been previously implanted under pentobarbital sodium/Innovar anesthesia. In fasted guinea pigs, the migrating myoelectric complex (MMC) was recorded from the small intestine and was observed to propagate aborally at a speed that declined with distance from the pylorus (range of speeds of the front of phase 3: 17.5 cm/min in the duodenum to 4.1 cm/min in the ileum). The complex was not disrupted by feeding but occurred less frequently in the freely fed state (82-min cycle period in the fasted state versus 139 min in the fed state). The complex started in the duodenum and was accompanied by a brief (6.3 +/- 0.9 min) period of inhibition of antral myoelectric activity. Slow waves were also recorded from the gastric antrum (10.3 +/- 1.3/min) and the small intestine. The frequency of intestinal slow waves was uniform along the length of the bowel (26.2 +/- 1.3/min in the duodenum to 24.7 +/- 1.3/min in the ileum). It is concluded that the guinea pig is similar to other mammalian species, so far examined, in its pattern of gastrointestinal myoelectric activity.