The execution of cancer clinical therapy trials has evolved over the past 45 years and is centered in the Clinical Oncology Group mechanism. The organization, statistical and administrative support, protocol development, and quality control systems have been worked out well and can be described in detail through the Eastern Cooperative Oncology Group. Prevention trials, on the other hand, are larger and fewer and take longer to complete. They involve people who are healthy or not as motivated to take pills or change lifestyle habits as those who are ill. The problems of compliance, toxicity, and costs become major issues. The practice of medicine is organized to take care of sick people and not healthy volunteers. We describe potential roles for Clinical Oncology Groups. These include preliminary tests of prevention agents for safety and toxicity much like Phase 1 trials with cytotoxic agents. A second important possible involvement would be to provide patients at high risk for developing second cancers, treatment- or non-treatment-induced, for prevention trials. A third set of individuals that can be recruited through current group resources are relatives of cancer patients who themselves might be highly motivated to participate in prevention trials. While the Clinical Oncology Groups may not have primary roles in prevention trials, they do represent a resource that has trial discipline and willingness and could facilitate the research efforts in chemoprevention.