A seroepidemiological study of human immune deficiency virus type 1 (HIV-1) and HIV-2/human T-lymphotropic virus type IV (HIV-2/HTLV-IV) infections was performed in Angola in October 1986. Until then five cases of acquired immune deficiency syndrome (AIDS) had been registered in Angola. During this study, another three cases with clinical AIDS were found and confirmed by HIV-1 serology. A total of 1,215 sera from groups of healthy persons and patients were tested for HIV-1 and HIV-2/HTLV-IV antibodies by enzyme-linked immunosorbent assays (ELISA). Sera positive by ELISA were also tested by Western blot (WB) analysis. In Luanda, the capital, HIV-1 antibodies were demonstrated in 0.4% (2/452) of male blood donors, in 0.3% (1/357) of pregnant women, in 1% (1/100) of tuberculosis patients, in 4% (4/94) of patients at medical wards, and in none of 22 women hospitalized with pelvic infections. In the Cabinda province, 11% (4/38) of postnatal women at a maternity ward were found to be HIV-1 seropositive, but only 2% (1/55) of other hospitalized patients and none of 32 male blood donors or 59 healthy persons in a village on the border to Zaire. Specific antibodies to HIV-2/HTLV-IV were not found in any of the sera. However, 16 out of 17 HIV-1 positive sera cross-reacted with HIV-2/ HTLV-IV core proteins by WB. In October 1987, 280 of the blood donors from Luanda were retested for HIV-1 antibodies and one of them was found to have seroconverted during the previous year. HIV-1 infection exists in Angola, but the prevalence in Luanda is lower than in the capitals of some neighboring countries in central Africa.