All 159 principal investigators whose projects had been assessed by the biomedical research ethics committee in Health Region 4 (Central Norway) during 1986-92 were asked to complete a questionnaire about medical research ethics and the work of the ethics committee. Their answers about scientific fraud and misconduct have been published previously. This paper reports how the 119 respondents (70% of those addressed) regard the role and work of the ethics committees and how they perceived the committee's assessment of their own project. A majority agreed that medical ethics committees are an important part of the scientific community (90%), that scientific quality is an important ethical element of any project (85%), and that researchers put more effort into their study protocol as they knew it would be assessed by an ethics committee (85%). More than 70% agreed that the committee's comments were useful and relevant, but a majority of these agreed only partly. The results are discussed in relation to the characteristics of the investigators.