Many potential markers, including biochemical markers, have been studied in an attempt to identify the presence of early colorectal neoplasia or risk of neoplasia, particularly in those families with hereditary colonic neoplasia syndromes. Unfortunately, most of these markers are useless in screening or diagnosis. Nevertheless, such markers as carcinoembryonic antigen (CEA) and CA 19-9 may have a role in pretherapeutic and posttherapeutic monitoring of disease or recurrence. The newer tumor markers, including the carbohydrate markers, ornithine decarboxylase (ODC) and the polyamines, are of great interest as potential tumor markers; ODC and the polyamines may also have a future potential as therapeutic targets. However, further studies are needed to determine their true sensitivity and specificity in hereditary colonic neoplasia syndromes, as well as in patients without genetic syndromes who are at risk for colorectal cancer.