The purpose of this project is to evaluate the incidence and etiology of post-transfusion hepatitis in newborn babies. Babies who recieve blood transfusions, primarily premature infants, and non-transfused control babies, are followed for six months after transfusion or hospitalization. Blood specimens are collected monthly during follow-up and are tested for alanine aminotransferase (ALT) level as evidence of hepatitis. Sera are also tested for serologic evidence of hepatitis A and B virus, cytomegalovirus or Epstein-Barr virus infection and are stored for testing of non-A non-B hepatitis agents which may be identified in the future. The goal of the project is to complete prospective follow-up of 200 recipients and 200 controls. The incidence and etiology of hepatitis will be compared in the two groups of babies and with data from a similar study (part of the Transfusion Transmitted Viruses Study) conducted among adults in the same institution.