We have examined the pharmacokinetics of 99mTc diethyl HIDA in five patients with a T-tube inserted into their common bile duct after choledocotomy. Blood clearance was rapid with 27.5% of the injected dose in the circulation at 2.5 min and 5% at 30 min. The peak bile excretion of 15.4% occurred between 45 and 60 min after injection of the HIDA. By 2 h 69% of the dose was excreted in the bile and 14% in the urine. In a second group of 33 patients a naso-gastric tube was passed after injection of HIDA. The patients drank 400 ml of 10% dextrose and aliquots of the stomach contents were aspirated every 10 min for an hour. In specimens with a pH greater than 4, the amount of HIDA correlated well (p less than 0.01) with the amount of bile acid determined by an enzymatic method.