Reviews the design and, where available, findings of 91 phase 3 studies using the randomized intervention trial design to evaluate the efficacy of measures for cancer prevention. By presenting and comparing the main features of these studies, the author aims to provide an early alert to methodological problems while also yielding clues about fruitful lines of inquiry. Ongoing as well as completed studies are included in this comprehensive review.Methodological issues are covered in the first chapter, which discusses three main types of intervention: chemoprevention, modification of lifestyle, and immunoprevention. Current trends in the recruitment of subjects and the choice of preventive intervention are also identified. The next chapter summarizes the results of several early studies, which although focused on the prevention of cardiovascular disease, included cancer mortality or incidence as an end-point. The third and most extensive chapter summarizes the results of 91 randomized intervention trials designed to assess the potential of specific interventions to prevent cancer. To facilitate comparison, studies are organized according to 10 major cancer sites and further grouped according to chemopreventive, lifestyle modification or immunopreventive intervention. Comparisons of related studies support a number of conclusions concerning the design of studies and the potential efficacy of specific interventions. The final chapter discusses current trends in the design of cancer intervention trials. Trends are reviewed in terms of the types of study design used at each cancer site, geographical areas involved in the trials, criteria for admission, end-points, and the agents and doses used for treatment.