Toxoplasmosis is a cosmopolitan disease. Our aim was to evaluate the epidemiological importance of toxoplasmosis in patients with acquired immunodeficiency syndrome (AIDS) and blood donors in Bamako (Mali, West Africa). A one year study of toxoplasmosis prevalence was carried out among patients with acquired immunodeficiency syndrome and blood donors in Bamako. The toxoplasmosis prevalence was 60% from AIDS patients, 22.6% from the HIV-seropositive blood donors and 21% from the HIV-seronegative blood donors. The specific antibodies were IgG and IgA. The specific IgM were not detected.