In order to improve the response rate of chemotherapy, we have investigated to the method for rapid and accurate prediction of the most appropriate anticancer agents. Thus, a rapid method using nude mice has been established as in vivo model for assessing chemosensitivity of individual human tumors, in which the final evaluation was made with 3H-thymidine incorporation and histological changes of tumor cells treated. Correlation between the sensitivity of anticancer agents and retrospective results of gastrectomy in stage IV gastric cancer was investigated. Our sensitivity test indicated a good correlation with clinical therapeutic and immunological effects. From these results, it seems reasonable to conclude that the sensitivity test using human tumor/nude mouse system may be useful for selection of appropriate agents to treat patients with cancer.