The controlled clinical trial is a relatively new phenomenon; the first large clinical trial on evaluation of streptomycin in therapy of pulmonary tuberculosis occurred in 1946. In such a study, two or more groups of patients with similar characteristics are chosen by random allocation to receive one or more therapies. The essential ethical dilemma is based on the risk-benefit ratio of the new therapy. Ethical factors that must be considered in the design of controlled clinical trials include provision for informed consent, nature of alternate therapy, confidentiality of data, source of funding and potential conflict of interest, remuneration of subjects, criteria for ending participation of the subject, criteria for concluding the trial, compensation of injured subjects, compliance with institutional, municipal, state and federal regulations and provisions for special groups such as the fetus and pregnant woman, infants and young children, institutional patients and prisoners. Federal guidelines for research in specific areas are now available through the reports of the National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research. To date, commission reports include recommendations for research in fetuses and pregnant women and in children. Protection of the subject is best provided by the quality of the protocol, integrity of the investigator, valid informed consent, and review of the research program by an independent committee composed of scientists and consumers.