Fifty-three tumor specimens, including thirty-one stomach and seven esophageal cancers, were examined to determine the individual tumor sensitivity to chemotherapeutic agents. Using the subrenal capsule assay (SRC assay), tumor specimens were implanted under the renal capsule of male, 8 week old ddY mice, after cutting the tissues into 1.5 mm cubed fragments. Following the implantations, chemotherapeutic agents were injected daily for 3 days and the relative variations of tumor weights were calculated. An 84.9 per cent of the total evaluability rate was obtained and implanted tumor specimens responded to chemotherapeutic agents in 26.7 per cent. The correlation rate between tumor sensitivity in SRC assay and clinical responses was obtained in 72.9 per cent. The predictive accuracy rate of the clinical responses was 50.0 per cent, while 100 per cent of the prediction rate of clinical resistance was obtained. With regard to upper gastro-intestinal cancers, 83.9 per cent of the evaluability rate and 18.2 per cent of response rate in SRC assay were obtained. These results indicate that this assay is equivalent to other procedures for predicting individual tumor sensitivity.