This article delineates the current status of clinical research into the chemotherapeutic treatment of advanced colorectal cancer. The data reviewed indicate that, despite an extensive series of trials, no new agents with significant activity have been identified. The most active single agent remains 5-fluorouracil (5-FU); efforts to enhance or modulate the activity of this drug with methotrexate, cisplatin, folinic acid, and N-(phosphonacetyl)-L-aspartic acid (PALA) are described. Of these approaches, combinations of 5-FU and folinic acid have been the most successful. Two recently reported studies suggest that patient survival is improved by this combination compared with 5-FU alone. Specialized applications of chemotherapy are also reviewed. Included is a description of the results of a recently conducted randomized trial of hepatic intra-arterial 5-fluorodeoxyuridine (FUDR) versus FUDR administered systemically. This study confirmed the improved response rate for patients receiving intra-arterially administered fluoropyrimidines but failed to substantiate a survival advantage over patients receiving intravenous therapy. Finally, newly evolving therapies such as hepatic-arterial chemoembolization, the use of new intra-arterial drugs, and high-dose systemic chemotherapy are reviewed. Directions for further clinical and basic scientific research are outlined.