The serum antibodies to human immunodeficiency virus types 1 (HIV-1) and 2 (HIV-2) were examined for among individuals who visited health centers in Tokyo. Of 8,198 sera screened, one was true-positive and 37 false-positive for HIV-1 antibodies. These 37 false-positives and 305 sera from the population groups at risk for HIV-2 (42 sojourners in Africa, 251 homo- and bisexuals, and 19 prostitutes) were further examined for HIV-2 antibodies by indirect immunofluorescence and Western blotting. No antibodies reactive with HIV-2 were detected in the sera examined. Serological cross-reactivity between HIV-1 and HIV-2 was examined by use of rabbit antisera.