In recent years an increasing number of antiretrovirals have become available. In order to define the optimal treatment regimens an increasing number of clinical trials are needed. Our objective was to study the profile of participants in HIV clinical trials in Europe and learn from their experience and views. Between August 1996 and September 1997, self-administered anonymous questionnaires were distributed to people with HIV infection at inpatient and outpatient clinics in 11 European countries. One thousand three hundred and sixty-six people completed the questionnaire (50% response rate). Four hundred and twenty (31%) of the respondents reported that they had previously participated in at least one HIV clinical trial. The percentage of people who had taken part in a clinical trial varied widely between the different centres, from 12% in Athens to 61% in Antwerp and Brussels. A significantly higher participation rate was observed in the northern and central part of Europe compared with the south (respectively 40% vs 18%) and also among people with a higher income. Most people (92%) stated that they were 'well' or 'very well' informed prior to enrolment in the trial. However, 4% reported that they had not given written approval and 22% felt that they were pushed into participating. Only 21% stated that they were informed about the outcome of the study on its completion. The most important reason for non-participation (37% of the non-participants) was because a clinical trial had never been proposed. In conclusion, a majority of people with HIV infection in European HIV treatment reference centres were willing to participate in clinical trials. HIV clinical trials in Europe should adhere more strictly to universal ethical standards.