Chemosensitivity testing is considered by some to be a useful method for predicting drug sensitivity of tumor tissues after surgery for gastrointestinal cancer. Although survival benefit is not fully established, several chemosensitivity testing methods have been used clinically, both in the selection of adjuvant therapy and in the treatment of metastatic disease. Chemosensitivity testing is used not only for determination of drug resistance, but also for determination of drug sensitivity conferring a potential survival benefit. Previous retrospective correlation studies showed survival of patients treated with a ‘tested’ drug to be superior to that of patients treated with a standard drug, but the clinical benefit of chemosensitivity testing in comparison to surgical therapy alone or standard chemotherapy has not been documented in a randomized controlled trial. The clinical usefulness of individualized versus standard therapy needs to be determined. Here we discuss the potential survival benefit and current limitations of chemosensitivity testing in patients with gastrointestinal cancer.