The campaign against the spread of the acquired immune deficiency syndrome (AIDS) in Switzerland includes a nationwide educational programme. A booklet about AIDS was mailed to every Swiss household in March 1986, and in 1987 there has been a mass media campaign promoting the use of condoms. We evaluated the results of the first phase--the distribution of the booklet--using a separate sample pretest and post-test design. The pretest was carried out 15 days before the booklet was mailed (sample n = 1056) and the post-test two months after the booklet was mailed (n = 1278). Of the population aged 20-69, to whom the book was sent, 56% read the booklet. For those who read the booklet compared with those who did not the results showed an improvement in knowledge and a better understanding of the risks of specific behaviours and of exposed groups and thus less fear of becoming infected through daily activities. The mean indices of knowledge and beliefs were significantly different when tested by the Kruskal-Wallis method. Having better information does not imply that people will change their behaviour, but both the high reading rate and the increase in knowledge suggest that the Swiss educational programme reached its objectives. Moreover, the success of this campaign helps to support other campaigns that are being developed to promote the use of condoms.