The presence of human herpesvirus 8 (HHV-8) DNA sequences was sought by polymerase chain reaction (PCR) in peripheral blood mononuclear cells of 4 groups: 6 human immunodeficiency virus (HIV)-infected persons with well-defined dates of seroconversion, during the period between the diagnosis of HIV infection and the appearance of Kaposi's sarcoma (KS); 45 HIV-positive persons with no symptoms of HIV infection; 11 AIDS patients with KS; and 14 AIDS patients without KS. HHV-8 DNA PCR was positive in 3 of the 6 patients during HIV infection preceding the appearance of KS and in all but 1 of 11 AIDS patients with KS. HHV-8 DNA PCR was negative in all but 1 of the 45 HIV-positive persons with no symptoms of infection and in all but 1 AIDS patient without KS. These results indicate that HHV-8 DNA may be detected several years before the occurrence of KS in HIV-infected subjects.