To evaluate the diagnostic value of faecal total bile acid determination in adult patients with chronic diarrhoea, output and concentration of 3a-hydroxy-bile acids were determined in 28 patients. The patients had normal results of primary biochemical, radiologic, and endoscopic examinations. Stools were sampled for 3 days while on a standardized diet. The patients were observed until final diagnosis was obtained; Crohn's disease was diagnosed in 5 cases, osmotic diarrhoea in 4, bacterial overgrowth in 3, laxative abuse in 2, other specific causes in 3, and persisting lack of specific diagnosis in 11. No difference in output or concentration of faecal bile acids was found between the groups. Six patients with high bile acid outputs benefited from treatment with cholestyramine. Accordingly, determination of total bile acids in stools cannot be recommended as a primary test in patients with chronic diarrhoea.