The usefulness of the nude mouse-human cancer xenograft system for a sensitivity test of chemotherapeutic drugs is evaluated. In our present study, the response of 9 experimental chemotherapies on 7 lines of cancer xenografts in nude mice was directly compared with clinical response in each donor patient, to the same chemotherapy and good correlation was found between these respective results. Experimental studies on chemotherapeutic effects on 14 lines of cancer xenografts (7 gastric, 3 colorectal, 3 breast and 1 pancreatic cancer) using 5 clinically active and 5 new drugs, were also conducted Although every line of xenograft retained different patterns of sensitivity to the various agents, drugs which were clinically effective to a type of tumor were found to be also sensitive against the same type of xenografts in nude mice. Thus the nude-mice human cancer system were is thought to be useful as a predictive secondary screening for new drugs. However, further improvement is necessary to establish this system as a more accurate selection method for anti-cancer drugs.