The effects of interruption of the enterohepatic circulation of bile acids on biliary lipid secretion have only been studied experimentally, and quantitative data in patients are lacking. Therefore, biliary lipid secretion during steady-state meal perfusion of the duodenum was studied in six patients with partial ileocolectomy, five patients with Crohn's disease, and five normal subjects. Bile acid outputs in the resection patients were significantly lower than in normal controls, (6.87 +/- 2.10 mmol/6 hr and 13.5 +/- 2.16, respectively; P less than 0.001) and were also decreased in two of the five Crohn's disease patients. Bile acid outputs in patients with resection progressively decreased in the course of the perfusion study; phospholipid and cholesterol secretion did not decrease to the same extent, and cholesterol saturation gradually increased. Bile of these patients, therefore, was frequently supersaturated due to uncoupling of bile acid secretion and outputs of the other biliary lipids. Bile acid outputs, although decreased, did not reach very low values, which shows that the enterohepatic circulation was not totally interrupted. Chenodeoxycholic acid was the main bile acid component of bile in patients with ileocolonic resection. Deoxycholic acid was absent from bile of four resected patients and two Crohn's patients. Two patients with active Crohn's disease had low bile acid outputs despite only moderate fecal bile acid losses. Therefore, decreased outputs may be caused by decreased bile acid pool not compensated for by increased bile acid synthesis in severely ill patients.