The adjuvant chemotherapy of colorectal and gastric cancer is being actively investigated. Studies of both single antineoplastic agents and combinations of several drugs have been used. In colorectal cancer, single-agent therapy has not resulted in improved survival. Combination chemotherapy studies are at too early a stage to be evaluated. In gastric cancer, single-agent chemotherapy has not been effective as adjunctive treatment to surgery. Combinations of active agents in gastric cancer hold promise as effective surgical adjuvant therapy.