Laboratory testing has the potential to favorably affect the outcome of patients with neoplasia by applications in screening, risk identification, surveillance, diagnosis, prognosis, prediction of tumor response or resistance to therapies, and prediction of toxic effects from therapies. Molecular testing directed at colorectal neoplasia is currently in use for diagnosis and characterization of rare, highly penetrant inherited syndromes due to germline mutation of the APC suppressor gene or DNA nucleotide mismatch repair genes. Routine application of molecular assays of colorectal tumors as prognostic and predictive markers is likely to occur in the near future, but major advances in technology are needed to begin to move molecular testing into screening of the general population and surveillance of subjects at increased risk. It seems certain that molecular methods will become increasingly important in improving the outcome of patients with colorectal neoplasia and in contributing to continued decline of the death rate from this common cancer.