The partial DNA sequence of a putative new herpesvirus has recently been isolated from almost all cases of Kaposi's sarcoma (KS), from a small subset of AIDS-related lymphomas, and from a high proportion of multicentric Castleman's disease. The presence of this KS-associated herpesvirus, which is also known as human herpes virus 8 (KSHV/ HHV8), has not been reported in vascular tumors other than KS. We therefore examined a series of vascular neoplasms of both endothelial and pericyte derivation using polymerase chain reaction to detect a 233-hp segment of the viral DNA. KSHV/HHV8 sequences were found in 7 of 24 (29%) angiosarcomas and 1 of 20 (5%) hemangiomas but not in any hemangiopericytomas (0 of 6). The presence of the virus in angiosarcoma was confirmed by direct sequencing of the polymerase chain reaction product and Southern blotting in one case each. Only one of the affected patients was known to be immunocompromised. By detecting its presence in a significant proportion of angiosarcomas, this study extends the number of tumors associated with KSHV/HHV8, further tightens its association with malignancy, and suggests a tropism of the virus for endothelial cells. The presence of KSHV/HHV8 in angiosarcomas in addition to classical KS also indicates that immunosuppression is not a requisite for viral infection.