From June 1994 to July 1996, 4100 pregnant women living in Yaounde, Cameroon, were tested for human immunodeficiency virus type 1 (HIV-1) and syphilis. The HIV seroprevalence was 4.2% (95% confidence interval (CI): 3.6%-4.8%), and that of antibodies to Treponema pallidum was 17.4% (95% CI: 16.3%-18.6%) (HIV infection was twice as common in women with positive syphilis serology) (7.2% vs 3.6%). Over the study period, the antenatal seroprevalence of syphilis remained stable, while there was an increase in the HIV seroprevalence rate. There was an increase in HIV seropositivity in women uninfected with syphilis between 1994/1995 and 1995/1996 from 2.9% to 4.3%. By the end of the study, HIV infection was no commoner in women with negative compared with positive syphilis serology. It is therefore postulated that HIV infection in Yaounde has entered the general, sexually active female population. We suggest that management of pregnant women in Cameroon should include routine screening for both HIV infection and other sexually transmitted diseases (STDs).