Introduction The clinical differentiation between neonatal hepatitis and atresia of the bile ducts continues to be a difficult one. In both conditions, obstructive jaundice usually makes its appearance one to three weeks after birth. In both, the patient may for a period of time appear entirely well, gain weight, and develop normally. Although splenomegaly is usually more striking in neonatal hepatitis, it cannot be used to differentiate the condition from atresia of the bile ducts. We have previously advocated open liver biopsy carried out as expeditiously as possible as the initial procedure, on the grounds that a widespread hepatitis made the patient a poor candidate for the prolonged anesthesia attendant upon an exploratory operation.1 After examination of the biopsy, if neonatal hepatitis could be ruled out, further exploration was indicated. The finding of two cases of obstructive jaundice in which bile duct atresia and the microanatomical picture of neonatal