Radical surgery with extended lymph node dissection is the first and only curative treatment of gastrointestinal cancer. Although the combined cancer chemotherapy has achieved 30%-50% response rates, a controversy still remains over the significance of the adjuvant cancer chemotherapy after surgery. To break through this limitation, we have introduced the chemosensitivity test to evaluate the appropriate adjuvant cancer chemotherapy for advanced gastrointestinal cancer. Our plural studies indicated that the chemosensitivity test would be useful in evaluating the appropriated adjuvant chemotherapy by increasing survival in the sensitive group. Recently, the molecular targets have been clarified for the conventionally available antitumor agents, e.g., thymidylate synthetase for 5-fluorouracil, ATP-binding cassette transporters for anthracyclines, glutathione-related detoxification for platins, and topoisomerase I for CPT-11, which will be applied for dinical use in evaluating the appropriate cancer chemotherapy. The chemosensitivity test is approved as "advanced clinical medicine" by the Japanese Ministry of Health, Welfare, and Labor in five institutes at present. Because complete dissection and chemosensitivity test-guided adjuvant chemotherapy will result in a survival benefit for patients with advanced gastrointestinal cancer, this test should be approved as "social insurance" for further wide clinical application.