DIFFERENTIATION between extrahepatic biliary atresia and neonatal hepatitis remains a difficult problem despite continuing additions to the armamentarium of function tests and greater knowledge of morphological changes in the diseased liver. These two conditions account for over 90% of all cases of obstructive jaundice encountered in the early months of life. Neonatal hepatitis is being reported with increasing frequency.1,2Among the cases which form the basis of this report, 75 infants with neonatal hepatitis and 60 with biliary atresia were admitted to the Hospital for Sick Children, Toronto, and similar numbers were recorded at the Children's Medical Center, Boston during the past decade. The liver biopsy differentiates neonatal hepatitis from congenital atresia of bile ducts in many, but not all cases.3Liver function tests are of limited value beyond indicating the presence of biliary obstruction and parenchymal abnormality. Exploratory laparotomy and cholangiography are therefore performed in a large