Colorectal cancer is a major problem in the United States and other developed countries. A safe and effective chemopreventive agent could reduce the burden of colorectal neoplasia. Curcumin, is a product that is derived from Curcuma longa. It has been used for thousands of years as a traditional remedy. Curcumin blocks a number of targets involved in tumor initiation, promotion, and progression, and is considered a promising chemopreventive agent. The investigators propose to enroll 40 patients after screening colonoscopy who will have rectal biopsies at baseline and after 4 weeks of curcumin 4 grams per day. The investigators will use microarray analysis to identify genes that are modified by curcumin that could be used as biomarkers in future chemoprevention studies. The study will also evaluate tolerability and toxicity.