Abstract Cholesterol-4- 14C, cholic acid-24- 14C, and chenodeoxycholic acid-24- 14C were administered to infants with extrahepatic biliary atresia, and excretion of isotope in urine and feces was followed. Fifteen per cent of the administered cholesterol was eliminated in a 17 day period. Twenty-four to 48 per cent of daily excreted isotope was recovered from feces as neutral steroids, mainly cholesterol. The isotope in urine consisted of labeled bile acids, mainly cholic and chenodeoxycholic acid. A minor part of the urinary isotope consisted of a complex mixture of different bile acids. After administration of cholic acid-24- 14C, 55 to 77 per cent of the isotope was excreted in urine in a 4 day period. Chenodeoxycholic acid-24- 14C was excreted very slowly and only 15 to 17 per cent of the isotope was excreted in a 4 day period. Less than 3 per cent of the administered isotope was excreted in feces. Cholic acid was found to be a metabolic end product, whereas 4 to 7 per cent of chenodeoxycholic acid was transformed prior to urinary excretion.