The broad objectives of the center are to examine the mechanisms of nonparenteral transmission of long incubation hepatitis and hepatitis associated antigen (HAA). It is hoped to characterize the distribution of HAA and anti-HAA antibody in different body fluids after naturally acquired infection with HAA. Carefully controlled studies will be conducted on the efficacy of specific immunoglobulin therapy in limiting the spread of HAA in susceptible contacts. Finally, if potentially effective and safe HAA vaccines become available, active immunization studies iwll be carried out in an appropriately selected susceptible population.