OBJECTIVES: I. Select patients with colon cancer and families at high-risk for colon cancer and collect leukocyte DNA, immortalized cell lines, plasma, and tumor specimens from these individuals and from control individuals. II. Develop patient education, counseling, and follow up plans for these individuals. III. Compare the frequency of defective DNA mismatch repair in individuals with familial colon cancer versus all colon cancers by using antibodies to the hMSH2 and hMLH1 protein products.