To conduct a multicenter epidemiologic study of the human retroviruses HIV-1, HIV-2, HTLV-I, and HTLV-II in volunteer blood donors from areas of the United States that were reportedly at high and medium or low risk for HIV. Also, to determine the prevalence of retrovirus seropositivity in first time blood donors; and the rate of retrovirus seroconversion in repeat blood donors as a measure of incidence of infection; to ascertain risk factors for antibody-positive donors; to characterize the blood donor population by geographic location, age, sex, race/ethnicity, and donation history to permit analysis on prevalence, incidence, and risk factors; to identify recipients of retrovirus-positive blood units and conduct clinical and laboratory follow-up of these recipients; and to establish a blood specimen repository for long-term storage of specimens from study donors and recipients for future testing.