This paper summarizes the results of two surveys assessing the changes in the sexual behaviour of homosexual men under the impact of AIDS in West Germany and West Berlin. The risk of possible infection is increasingly taken into account by gay men in the Federal Republic. Regular use of condoms has already gained widespread acceptance—considering the short time available to become familiar with such usage. Attitudes to the risk of infection are chiefly determined by the impact of AIDS in the immediate social environment, by the extent of social integration in a network of supportive groups and by the degree to which the homosexuality of gay men is accepted by their social environment. In spite of the high level of information about AIDS that most gay men have at their disposal, and the widespread adoption of low–risk sexual practices, it remains apparent that certain subgroups are still not being adequately reached. ‘Closeted’ homosexuals, homosexuals with low educational and professional status and bisexual men are substantially less well informed than selfndash;identifying gay men with higher educational and professional status. Concepts that better appeal to and better inform these groups are urgently required. The demographic .group ‘males with homosexual behaviour’ can only be reached to a limited degree by targeting it as a homogeneous group