The present study has investigated whether Kaposi's sarcoma (KS) in Nigeria is associated with infection with the AIDS virus variously called human T-cell lymphotropic virus type III (HTLV-III), lymphadenopathy/AIDS virus (LAV), and AIDS-associated retrovirus (ARV). Serum samples from 40 KS patients, 30 patients with malignant melanoma of the foot (contemporaneous controls), and 50 normal nontumour-bearing controls were tested for anti-AIDS virus antibody by enzyme-linked immunosorbent assay (ELISA). The assay consistently and reproducibly failed to show seropositivity in all the patients and controls. These results show that Kaposi's sarcoma in Nigeria is not associated with infection with the AIDS virus and that the virus is not endemic in this region.