A technique for the quantitative assessment of post-prandial duodenogastric bile reflux is described using a single isotopes 99Tcm and a single-channel large-field gamma camera with a data processing system. The stomach is localised with pertechnetate prior to IDA administration and duodenogastric reflux is calculated as the percentage of hepatic IDA output reaching the stomach after correction for background activity and hepatic overlap. The technique has been validated, and used to study reflux in 25 patients with gallstones and in 10 control patients. Gall bladder function was assessed with an oral cholecystogram. Marked reflux (greater than 7%) occurred in 5 out 9 patients with a non-functioning gall bladder but in no controls and in none of 16 patients with gallstones in a functioning gall bladder. When patients were studied again after cholecystectomy, 2 patients with normal functioning gall bladders had developed marked reflux while those with preoperative reflux continued to reflux after cholecystectomy. Symptoms of gallstone dyspepsia before operation were more severe in those with marked reflux than those without. Surgery improved these symptoms even in those who continued to reflux after operation.