All graduating physicians in the U.S.S.R. take an oath that since November 1983 has included a pledge to work for peace and the prevention of nuclear war. The authors compare the Soviet oath with those taken by American physicians, none of which mentions nuclear war, and give reasons why the medical profession in the Soviet Union may be more sensitive to this issue than its American counterpart. They explore the rationale behind professional oaths and codes, and identify changes in how physicians in the United States regard their responsibilities vis-à-vis individual patients and the public. Arguing that nuclear weapons pose the greatest threat ever to public health, Cassel et al. propose incorporating a commitment to work to prevent their use into the oath taken by American medical school graduates.