In order to determine the proportion of tuberculosis (TB) patients in Bangui (Central African Republic) infected with human immunodeficiency virus (HIV), we collected prospectively serum samples from all new TB patients seen at the University Hospital in Bangui during a three-month period (nov. 87-Jan. 88). 220 serum samples were tested for antibodies to HIV, by an Elisa assay and confirmed by Western-Blot. The general HIV seropositivity rate among TB patients was 27.7% (31.2% in adults (N = 183), and 10.8% in children (N = 37)). Within the adult population, there was non association between HIV infection and sex or previous history of TB. Seropositivity was more common in patients with extrapulmonary TB, especially lymphadenitis, and in patients with mediastinal adenopathy, or extensive pulmonary involvement without cavitation. Seropositivity was also strongly associated with negative tuberculin skin tests, chronic diarrhoea, generalized lymphadenopathy, and thrush. It is concluded that HIV infection is responsible for the increasing incidence of tuberculosis in Central African Republic, and that investigations for TB should be carried out in every symptomatic African patient infected with HIV.