Kaposi's sarcoma (KS), a vascular tumour that contains characteristic spindle cells forming slit-like spaces, may have an infectious aetiology. Recently, sequences of a new human herpesvirus, KSHV/HHV-8, have been identified in both HIV-associated and classical KS. We sought to identify the target cell of this virus in KS tumour tissue. Using PCR in situ hybridization (PCR-ISH) we show that KSHV/HHV-8 is present in the flat endothelial cells lining vascular spaces of KS lesions as well as in typical KS spindle cells. These findings show that KSHV/HHV-8 is present in the cell types thought to represent neoplastic cells in these lesions.