In this study we evaluated the effect of enteric hormones on sphincter of Oddi and gastrointestinal spike burst frequency in fasted conscious opossums. A chronic model for obtaining multiple long-term recordings of sphincter of Oddi and gastrointestinal myoelectric activity was prepared in 12 animals by implanting bipolar electrodes in the gastric antrum, duodenum, sphincter o f Oddi, jejunum, and ileum. Subsequently, 8–18 recording sessions, 6–8 h in length, were obtained in each animal. Each study was preceded by a 15-h fast. After recording two cycles of the interdigestive migratory myoelectric complex, a 60-min infusion of saline, cholecystokinin-octapeptide, pentagastrin, glucagon, or secretin was begun early in the quiescent period of duodenal activity, 10 min after termination of phase 3 of the migratory myoelectric complex activity. Cholecystokinin-octapeptide (10–80 ng/kg · min) and pentagastrin (25–200 ng/kg · min) increased sphincter of Oddi spike burst frequency while converting interdigestive gastrointestinal myoelectric activity to a fedlike pattern of continuous, irregular spike bursts. Glucagon at high doses of 500 and 1000 ng/kg · min depressed sphincter of Oddi and gastrointestinal spike burst activity, whereas lower doses of glucagon and secretin (3–12 CU/kg · h) had no effect. We conclude that in the opossum, relatively low doses of cholecystokinin-octapeptide and pentagastrin stimulate sphincter of Oddi and gastrointestinal spike burst activity while disrupting the cyclic pattern of sphincter of Oddi and gastrointestinal spike burst activity present during fasting. The physiological significance of these findings remains to be determined.