In determining the effectiveness of AIDS preventive measures among heterosexuals, trends in visits to two clinics for sexually transmitted diseases (STD) in Amsterdam between 1982 and 1989 are described. Also, data on sexual behaviour are presented that were collected in a sample of 635 heterosexual women and 947 heterosexual men at one of the clinics between September 1986 and December 1988. In 1987, when in The Netherlands for the first time extensive publicity was given to the risk of heterosexual transmission of the human immunodeficiency virus, the numbers of male and female heterosexual attenders started to decline. Exceptions to this general decline were men of Turkish nationality and foreign prostitutes, each group showing a continuing increase. At the same time, the numbers of customers reported by prostitutes in the sample declined markedly between 1986 and 1988, from a median of 35 to 15 per month (p = 0.001). Condom use with casual contacts generally increased in the sample period. We conclude that the publicity given to "heterosexual AIDS"--contributed to by the national AIDS prevention campaign--apparently led to a considerable decrease in the number of risky contacts of heterosexuals in Amsterdam in 1987 and 1988. This does not seem to apply to men with Turkish nationality. In 1989 a change appeared in several subgroups when the number of visitors started to rise. Also, the probability of an STD diagnosis increased in male attenders. This may indicate a change in the tendency towards safer sexual behaviour.