This is an exploratory, laboratory-based evaluation of cellular immune response to immunization with hepatitis B surface antigen in HIV-infected and HIV-uninfected adolescents. This is a substudy of ATN 024 and ATN 025. This substudy will compare cellular immune response in responders and nonresponders to immunization and also evaluate the relationship of these factors to the persistence of known correlates of serologic protection for the hepatitis B virus.