Heterosexual bidirectional transmission of HIV is now clearly proved. In Western countries, and in particular in Belgium, the existence of clusters of heterosexual transmission demonstrates that, as in Central Africa, the epidemic could spread among heterosexuals. Sexual contacts with partners who belong to different high risk groups for HIV may introduce the virus in the general population. This is mainly true with bisexual men, IV drug users or people originating from endemic areas. Prostitutes are also at high risk to be infected and to transmit HIV. Prevention campaigns toward heterosexuals should begin at a pre-epidemic stage and focus on counselling of infected individuals, voluntary testing of contacts of these subjects and selected screening programmes.