Bile salt pool size and kinetics were evaluated in 8 morbidly obese women before and following jejunoileal bypass. The results indicate that following jejunoileal bypass pool sizes of both chenodeoxycholate and cholate decrease, turnover rates increase, and the rates of bile salt synthesis increase. Influenced by pool size, hepatic synthesis and the degree of malabsorption, the daily bile salt loss may actually decrease in time. Chenodeoxycholate is more efficiently absorbed than cholate in both the preoperative and postoperative states. In spite of greater cholate synthetic capabilities, in this malabsorptive state the chenodeoxycholate pool decreases less than the cholate pool. Although all patients received an identical surgical procedure, the effect on bile salt kinetics and pool sizes varied in these patients. Since some of the postoperative complications may be related to the degree of interference with bile salt metabolism, the individual patient's capacity for increased hepatic synthesis of bile salts and increased reabsorption of bile salts from the remaining small bowel may vary the clinical postoperative course.