Immunohistologic studies were performed to evaluate the expression and regional distribution of 20 colorectal carcinoma-associated antigens in the colonic mucosa of 12 normal adults. A distinct regional variation was seen in the expression of blood group A, B, Lewis(b), and extended Lewis(y) antigens, which were expressed predominantly in the right colon, whereas Lewis(a), Lewis(y), and H-type 2 were prevalent throughout. Lewis(x) and X-like antigens were only occasionally expressed. Two antibodies against sialylated Lewis(a) showed different staining patterns, with CA19.9 positive in only two biopsies and CO29.11 intensely positive in most. Two of the three antibodies detecting carcinoembryonic antigen epitopes (3d6 and COL-4) stained many biopsies, whereas COL-12 was rarely detected. No regional gradient was found in the expression of the other antigens studied (B72.3, ME491; GA73.3, ND1, and ND4). This mapping data will provide an important baseline for future studies of epitope distribution in the colon in premalignant and neoplastic conditions.