Resection of the distal 30% of the small intestine in dogs caused a decreased gallstone dissolution rate and phospholipid/ cholesterol (P/C) ratio when compared to that of the controls. This effect was not seen in animals with 10% distal ileal resection or those fed cholestyramine resin, which binds bile salts in the intestine. The incidence of cholelithiasis in a survey of 52 patients with regional ileitis or distal ileal resection was 26.8%. This is greater than twice the incidence (11%) found in a comparison group of 75 patients. The mechanism of the association of cholelithiasis with regional ileitis or distal ileal resection is most likely the result of the formation of lithogenic bile due either to the decreased P/C ratio or an increase in the glycine/taurine ratio.