Seventy-five married men found to be positive for HIV-1 in Harare, Zimbabwe, were interviewed in order to define behaviours associated with acquisition of infection and to determine factors associated with transmission of infection to their wives. The majority of infected men reported sexual intercourse with multiple heterosexual partners and female prostitutes, and gave a history of sexually transmitted diseases (STDs). All subjects denied homosexual activity and parenteral drug abuse. Serological testing of the wives of seropositive men showed that 45 (60%) were HIV-antibody-positive. Wives of men with AIDS and AIDS-related complex (ARC) and wives of men who gave a history of genital ulcer disease were more likely to be seropositive. The study demonstrates that HIV-1 infection in Zimbabwe occurs through heterosexual intercourse and is associated with other STDs. In addition, the study shows that male to female transmission of HIV-1 is facilitated by the presence of genital ulcers in infected men.