Fecal excretion of labeled bile acid (14C-24-cholic acid) was distinctly increased in two infants with protracted diarrhea, whereas four patients with steatorrhea due to pancreatic or mucosal abnormalities and five patients with mild chronic diarrhea had no excess fecal loss of bile acid. The loss of 14C-24-cholic acid in our patients with intractable diarrhea was similar to that observed in four infants who had undergone ileal resection. The ratio of mean 24-hour excretion of bile acid to that of a non-absorbable marker, polyethylene glycol, confirmed the malabsorption of bile acid in the patients with intractable diarrhea or ileal resection. These results differ significantly (p less than 0.05) from excretion ratios obtained in patients with either steatorrhea or chronic diarrhea. The extent of the loss of bile acid was not significantly related to the rate of fecal fat excretion. There was no direct correlation of fecal weight with the rate of bile acid excretion. Ileal function, as further assessed by the Schilling test with exogenous intrinsic factor, was grossly abnormal in both of the patients with intractable diarrhea.