Abstract
The managerial structure of collaborative studies is usually not described in reports presenting results from such investigations. The same is true about the experience obtained in the day to day conduct of such studies. Ethical rules which should govern collaboration between individuals and centres are rarely spelled out. The paper presents an outline of WHO's mental health programme and proposes, on the basis of experience obtained in the course of several WHO multicentric international studies, a set of guidelines concerning ethical aspects of scientific collaboration involving several centres or teams.