Two hundred and forty-one prostitutes working in The Cambia were tested for retroviral infections and their immune system evaluated. Sixty-three were seropositive for HIV-2 only, five for HIV-1 only and six for both HIV-1 and HIV-2 (26.1, 2.1 and 2.5%, respectively). When compared to seronegative individuals, the 63 women infected with HIV-2 clearly had an abnormal immune system, with significantly lower CD4 + and higher CD8 + lymphocyte counts and percentages, lower CD4 +: CD8 + ratios, lower CD25 + (activated) lymphocyte counts, and lower lymphocyte proliferation responses after stimulation with phytohaemagglutinin, purified protein derivative (PPD), Candida or pokeweed mitogen, and higher levels of neopterin and β2-microglobulin. However, when the HIV-2-seropositive prostitutes were compared with the five women infected with HIV-1, the former were less abnormal, with significantly higher CD4 + percentages and CD4+: CD8+ ratios and lower CD8 + percentages and counts. Immunological anomalies were seen in five women known to have been infected with HIV-2 for <17 months. Coinfection with HTLV-I resulted in more severe immunological alterations than infection with HIV-2 alone.