The field of ethics in medical research has seen important developments in the last three decades, but it also faces great challenges in the new century. The purposes of this report are to examine the current status of ethics of medical research involving human subjects and the nature of the ethical challenges facing this research, to identify the weakness of the current system of safeguards for ethical research, and to stress the importance of the ethical character of the researcher, which is the safeguard that has the greatest potential for protecting the research subjects. Researchers appreciate the risks of human medical research that create ethical dilemmas and the need for an ethical compromise in order to proceed with the research. The main elements of the compromise, formulated primarily from experiences in the Second World War, include: (1) the dominant position of the ethical principle of autonomy; (2) the demand for a signed informed consent; (3) the likelihood of improving health with the research protocol, which must be approved by a duly appointed supervising committee; and (4) an acceptable risk/benefit ratio. The main weakness of this set of safeguards is the difficulty with obtaining a truly informed consent. The new challenges to ethical medical research stem from certain types of research, such as genetic and stem cell research, and from the increasing involvement of the industry in planning and funding the research studies. Developing medical researchers with an ethical character and knowledge about ethics in medicine may be the most effective safeguard in protecting participants of medical research experiments.