An association between diet and colorectal cancer continues to be supported by animal experimentation and human intervention trials. The significant absence of vegetables of the Cruciferae or cabbage family in the diet of colon cancer patients suggests that these vegetables may aid in the prevention of colorectal cancer. The induction of detoxification enzymes by cruciferous vegetables and the isolation of vegetable components with chemopreventive activity suggest the potential use of cruciferous vegetables as a chemopreventive intervention in patients at high risk for colorectal cancer. A pilot study is proposed to evaluate the ability of cruciferous vegetables to elevate the levels of detoxification enzymes within human colon mucosa. Individuals who have been scheduled for a sigmoidoscopy or colonoscopy procedure will be asked to participate in this study. Eligible subjects will include patients with a family history of colorectal cancer, patients with colon polyps and patients who are at increased risk for recurrent disease. Patients (N = 75) will be randomized into three groups and will either refrain from eating cruciferous vegetables (control), increase their consumption of cruciferous vegetables to one serving per day (Group I) or ingest six tablets of dried broccoli daily (Group II) for two weeks. The use of tablets should maximize compliance and standardize the dosage required in future clinical trials, particularly if chronic administration is indicated. The activity and expression of glutathione S-transferase and DT-diaphorase in colon biopsies taken before and after dietary intervention will be determined and compared. The enzymes selected for evaluation play a critical role in protecting cells against carcinogen exposure. Results obtained from Intervention Groups I and II will be compared. The enzymatic response of blood lymphocytes (from the same individual) to cruciferous vegetable supplementation will be assessed. Establishment of a correlation between this response and that of colon mucosa will support the future use of blood lymphocytic enzyme levels as a non-invasive measure of the responsiveness of colon mucosa. Future clinical intervention trials in high-risk cancer patients will assess the ability of cruciferous vegetables to inhibit the development and recurrence of colorectal tumors.