Bile acid metabolism was examined in two children with bile acid malabsorption, who were being treated with intravenous hyperalimentation. Fecal bile acid excretion was 1,261 mumol/m2/day in a child with bile acid malabsorption of unknown origin, and 1,877 mumol/m2/day in a child with secondary bile acid malabsorption after an operation for long-segment aganglionosis. These values were approximately 10 times higher than those in diarrheal or nondiarrheal children without apparent abnormalities in bile acid metabolism. Fecal bile acids in these patients with bile acid malabsorption were almost completely conjugated, with little unconjugated bile acid present. It is possible that the disturbed bile acid deconjugation in the intestine might be caused by a rapid intestinal transit time, which was found in our patients with bile acid malabsorption. In the analysis of biliary lipid composition, children with bile acid malabsorption were shown to have a chenodeoxycholate-dominant pattern, an increased glycine- to taurine-conjugated bile acid ratio, and markedly supersaturated cholesterol. Such profiles may be related not only to bile acid malabsorption but also to cholestasis, presumably due to intravenous hyperalimentation.