Randomized clinical trial is currently thought to be the most reliable method for comparing therapeutic effects. The article tries to ansewer the question whether chance allocation of patients into various therapeutic arms is acceptable from the ethical point of view. It deals with the conflict between two concepts: of individual ethics mostly defending interests of individual participants of each trial, and collective ethics based on well-designed experiments that are the sole source of reliable estimation of therapeutic effect and their conclusions can change clinical practice and help patients in the future. The article suggests this possible solution: providing there is no prevailing consensus as for superiority of one of the compared therapies, the offer to participate in randomized clinical trial is not only acceptable but necessary in view of individual patients’ right and respect of their autonomy. If an informed consent is obtained the principles of medical ethics have not been violated. Finally, a few alternative trial designs are presented.

        Key words: randomized clinical trial, statistics, ethics, informed consent, treatment preference, study design.