The excretion rate of fecal bile acids was determined by gas-liquid chromatography in nine patients with Crohn's disease and six healthy volunteers under two dietary conditions with different amounts of fat: during nasoduodenal tube feeding with a fat-restricted elemental diet containing approximately 1.5 g/day of fat, and during the addition of 50 g/day of butterfat by peroral administration. The fecal bile acid excretion rate on the elemental diet was significantly greater in the patients with Crohn's disease than in the healthy controls. With ingestion of the additional fat, the excretion rate was significantly increased in the patients with Crohn's disease, but not significantly changed in the healthy controls. The bile acid excretion rate in Crohn's disease correlated with fecal fat excretion, but not with either fecal weight or disease activity. These studies show that the amount of dietary fat represents an important consideration in the evaluation of bile acid malabsorption in Crohn's disease.