Sera from 37 adult Nigerian men with Kaposi's sarcoma (KS), 30 contemporaneous controls bearing primary cell carcinoma of the liver (PCL), and 150 healthy non-tumour-bearing negative controls were tested for antibody to human T-cell lymphotropic virus type III/lymphadenopathy associated virus (HTLV-III/LAV) by enzyme-linked immunosorbent assays (ELISA). Certain immunocellular functions were also measured: the chemotactic locomotion of peripheral blood monocytes towards casein, delayed-type cutaneous hypersensitivity reaction to tuberculoprotein and opportunistic infection with the fungus Candida albicans. Sera from all these groups were also tested for markers of previous infections with the viruses cytomegalovirus (CMV), Epstein-Barr virus (EBV), hepatitis B (HBV) and hepatitis A (HAV). All serum samples tested were reproducibly and consistently negative for anti-HTLV-III/LAV. Peripheral blood monocytes from both KS and PCL patients showed profound depression of chemotaxis; similarly all tumour patients gave markedly depressed cutaneous reactivity to tuberculoprotein and uniformly exhibited seropositivity to CMV, EBV, HBV and HAV. A great majority showed evidence of infection with Candida albicans. It is concluded that tropical African KS is not associated with HTLV-III/LAV infection.