We have observed several mesenchymal proliferative disorders (MPD) in macaques with SAIDS associated with SRV-2 infection. Retroperitoneal and subcutaneous fibromatosis, progressive fibrovascular proliferation, mimicking Kaposi's sarcoma, were seen in 165 macaques. Three obliterative fibrointimal proliferative arteriopathies and one congenital pulmonary sequestration with extensive MPD were observed in SRV-2 positive monkeys. Continuous cell lines were established and SRV-2 was identified in all tissues and cell lines. Immunophenotyping of the cultured cells showed heterogeneous mesenchymal cells. Xenograft and allograft transplantation of cultured cells produced MPD lesions in the recipients. The data suggest that SRV-2 plays an important role in the etiopathogenesis of MPD in macaques.