Feeding initiates gallbladder emptying and bile delivery into the duodenum. It is not yet defined how the sphincter of Oddi regulates flow of bile into the duodenum during gallbladder emptying. The aim of this study was to assess postprandial spike burst activity in the sphincter of Oddi, while quantitating gallbladder emptying with noninvasive radioisotope imaging. Six adult opossums were prepared with bipolar electrodes in the sphincter of Oddi. After 2 weeks of recovery the animals were fasted overnight and positioned under a gamma camera, and myoelectric recordings were begun. After two cycles of the migrating motor complex (MMC), 2 mCi 99Tc-HIDA was infused intravenously and permitted to concentrate in the gallbladder for a period of 30 min. Subsequently, a 30-ml liquid meal, containing 0.9 g protein, 3.5 g carbohydrate, and 3.3 g fat, was instilled into the stomach. Sphincter of Oddi myoelectric activity (spike bursts/min) and gallbladder emptying (expressed as percentage of original 99Tc counts in the gallbladder) were measured at intervals for 120 min following feeding. Feeding resulted in prompt gallbladder emptying. Sphincter of Oddi spike burst activity was not altered significantly in the first 30 min after feeding, suggesting that motor activity in the sphincter of Oddi does not initially influence bile flow. Subsequently, spike burst activity increased progressively, suggesting that sphincter of Oddi motor activity may accelerate bile delivery into the duodenum during later phases of gallbladder emptying.