The association between a new human herpesvirus-like agent and various forms of Kaposi's sarcoma was examined by PCR. The DNA sequences of this agent were detected in 7 of 8 classic Kaposi's sarcoma specimens, 12 of 12 AIDS-associated specimens from the United States, and 7 of 10 specimens from African endemic Kaposi's sarcoma. Polymorphism of the herpesvirus-like DNA in the Kaposi's tissue from different populations was observed by both single-strand conformational polymorphism and direct sequencing. Furthermore, the presence and expression of the virus was detected in some Kaposi's tumours by Southern and northern blotting. This herpesvirus may be involved in the pathogenesis of different kinds of Kaposi's sarcoma seen among distinct and unrelated populations.