Most recent evidence suggests that human herpesvirus 8 (HHV-8) infection is restricted to persons with Kaposi's sarcoma (KS) or to persons who may subsequently develop KS. To accurately determine the prevalence of infection in the United States, children and adults with AIDS were examined for evidence of HHV-8 infection to see whether HHV-8 (like other herpesviruses) would be readily detected in immunosuppressed persons. By use of nested polymerase chain reaction, DNA specific for HHV-8, Epstein-Barr virus, and cytomegalovirus was detected in blood leukocytes from 0, 26 (51%), and 9 (18%), respectively, of 51 children. Similarly, HHV-8-specific antibodies were not detected in analyses of sera from the children. By contrast, HHV-8 DNA was detected in 9 (27%) of 33 adult AIDS patients without KS. These findings suggest that the pattern of transmission of HHV-8 in the United States differs from that of other herpesviruses in that primary infection occurs predominantly in adults.