Cancer of the large bowel — colon and rectum — is a disease of the affluent, westernized cultures of Europe, North America, Australia, and New Zealand. In most of these countries large bowel cancer ranks between the first five, 1 and in countries such as the U.S. and Denmark colo-rectal cancer now represents one of the largest cancer problems when considering both sexes together. Both colon and rectum cancers rank among the leading cancer sites in those two countries in both sexes (Figure 1) with colon ranking only second to cancer of the breast in women in both Connecticut and Denmark, and with both colon and rectum cancer among the first six sites in men in these two registries. 1,2