OBJECTIVES: I. Determine whether high-dose folic acid decreases global DNA hypomethylation, as well as other intermediary markers, in normal-appearing colonic epithelium of patients with colonic adenomas. II. Determine whether a decrease in global DNA hypomethylation and other intermediary markers can be induced safely and whether these effects persist after folic acid is discontinued in these patients. III. Confirm pilot data that indicates patients with adenomas have widespread DNA hypomethylation of the colorectal mucosa compared to controls. IV. Evaluate the effect of folic acid on the clinical course and rate of recurrence of adenomatous polyps in these patients. V. Study a control group of patients with no history of neoplastic, hyperplastic, or inflammatory colorectal lesions.