A series of 223 patients undergoing cholecystectomy has been studied. In 204 patients the common bile duct was perfused with saline at a pressure of 30 cm. The rate of flow has been analysed as a means of determining the presence of common bile duct stones, this being confirmed on the evidence of operative cholangiography or exploration of the duct. The results suggest that flow studies can be more consistently obtained than cholangiograms, which were not available for technical reasons in 8.0 per cent of patients in this series. The results of flow studies are comparable with those of cholangiography in confirming the normality of the common bile duct but are less reliable in detecting stones. The reliability is such that if radiological facilities are not available, flow studies are an acceptable alternative. In none of these patients was stenosis of the sphincter of Oddi detected. If this clinical entity does exist, it is rare and of little significance.