Sixty-eight lorry drivers and their assistants were examined for evidence of infection with HIV-1 because of their association and regular contact with prostitutes. Out of a total of 68 drivers, 24 (35.2%) were serologically found to be HIV-1 positive. Epidemiological evidence demonstrated a wide travel history involving seven different countries served by the port of Mombasa. History of other sexually transmitted disorders were significantly higher in HIV-seropositive individuals. The data presented here further support the hypothesis that a major route of heterosexual transmission of HIV in Africa is dissemination through a group such as lorry drivers and their assistants, whose behaviour puts them at risk of acquiring sexually transmitted diseases.