140 consecutive African, exclusively heterosexual, adult outpatients to the Clinique des Maladies Sexuellement Transmissibles, with genital ulcers or urethritis, were studied in order to determine the status for HIV1-infection and syphilis. Comparison with 194 age and sex matched subjects, without STD, were chosen as controls. In the "STD"'s population, the HIV1 seroprevalence was 17.8%, and anti-treponema antibodies were found in 30% of the cases. Patients with genital ulcer were associated with a higher HIV1 seroprevalence than patients with urethritis. The "STD"'s population in Bangui is at risk for HIV1-infection (risk ratio: 2.12), and constitutes probably a very sensitive group in Central Africa for the epidemiological survey to HIV infection, and for the estimation of the prevention against AIDS.