The question "When are research risks reasonable in relation to anticipated benefits?" is at the heart of disputes in the ethics of clinical research. Institutional review boards are often criticized for inconsistent decision-making, a problem that is compounded by a number of contemporary controversies, including the ethics of research involving placebo controls, developing countries, incapable adults and emergency rooms. If this pressing ethical question is to be addressed in a principled way, then a systematic approach to the ethics of risk in research is required. Component analysis provides such a systematic approach.