Prostate cancer is the most common male malignancy in western countries. Although primary prevention of prostate cancer is not possible, screening using prostate-specific antigen (PSA) may eliminate prostate cancers by definitive treatments. Prevention of clinically detectable prostate cancer requires earlier chemoprevention interventions. Because prostate cancer is histologically present in 30-50% of 30- to 50-year-old men, effective chemoprevention needs to inhibit not only prostate carcinogenesis but also growth and progression of these cancers. A prostate carcinogenesis animal model has been used to screen chemopreventive agents; inhibitory effects were found with 9-cis-retinoic acid, dehydroepiandrosterone, fluasterone, and the Bowman-Birk inhibitor and an isoflavone mixture which both occur in soy. Such results can be used to select agents for clinical trials. Besides large-scale long-duration prevention trials, trials of short/intermediate duration using smaller cohorts prior to or following radical prostatectomy may provide excellent and cost-effective approaches for chemopreventive agent efficacy testing. Intervention prior to surgery allows measurements of intervention agents and intermediate end-points in the prostate. These peri-surgical trials only assess inhibition of growth and progression of preexisting cancer, not real preventive effects, but they focus on clinically significant cancers. Such trials are an essential step in the development of antiprostate cancer chemoprevention agents.