The years 1982-1992 have been selected because TAH incidence in adults was still high at that time and because all subjects would be under age 15 at enrollment and unlikely to have been exposed to sexual contact or IV drug use. Maternal testing is performed to exclude perinatal transmission. Sixty-five hundred children who meet the eligibility criteria of the study have been transfused at Children's National Medical Center (CNMC) during this period, and archival serum specimens are available for 22 percent. The total eligible cohort is contacted and asked to provide a blood sample that is tested for antibodies to HCV and to the newly discovered hepatitis G virus (HGV). Subjects found antibody positive on initial screen are enrolled in long-term followup that includes serial determinations for alanine aminotransferase (ALT), other liver-related assays, viral serology with confirmatory testing, PCR for HCV and HGV RNA, HCV genotyping and, in those with evidence of chronic hepatitis, liver biopsy. Biopsy may also be performed on a subset with chronic viremia, but normal ALT, pending approval of an advisory panel of liver experts. A serum repository will be established for evaluation of new diagnostic methods for HCV, HGV, and other etiologic agents of posttransfusion hepatitis.