‘Research on human subjects’ considers the Nuremberg Code (1947), which gave way to the World Medical Association's Declaration of Helsinki (1964). The Declaration (last revised in 2008) has no legal force in itself, but has had profound influence on national and international research ethics and law. It emphasizes the importance of autonomy and informed consent, and insists that the subject's welfare outweighs the welfare of society or the march of science. The various articles of the Declaration that are concerned with unknown risks, when research should stop, children and incompetent adults, and payment for medical research volunteers are discussed. Finally, the role of research ethics committees is reviewed.