Cell proliferation has an important role in carcinogenesis. Increased ornithine decarboxylase (ODC) activity with resulting polyamine synthesis is a phenomenon common to cells undergoing rapid proliferation and to models of tumor promotion. In colon cancer, bile acids are considered to be important tumor promoters. Inferential data suggest that bile acids can increase ODC activity and stimulate or alter cell proliferation in the large bowel. These changes may underlie tumor promotion by bile acids. Confirmation of this relationship will solidify this concept and build a framework for understanding the mechanism of bile acid promotion in colon carcinogenesis.