From 1 July to 31 December 1988 risk factors for HIV infection were systematically recorded for all individuals tested anonymously at our institution and compared with similar data observed when anonymous testing was introduced (1985-1986). The absolute number of homosexuals and intravenous drug abusers remained stable but their ratio decreased because most tests are now performed in persons with multiple heterosexual partners. More than half of heterosexuals said they used condoms. Tests were positive only in homosexuals and intravenous drug abusers. These data suggest that the ongoing Swiss nationwide educational programmes have been successful in reaching people potentially exposed to HIV. Such campaigns may still prevent the dissemination of HIV infection to the heterosexual population.