Preliminary clinical trials were conducted to determine the usefulness of the 6-day subrenal capsule assay (SRCA) as a predictor of response to chemotherapy. Evaluability rate was 87.6% in 130 surgical specimens obtained from various solid malignant tumors. Forty three SRCA were prospectively observed for accuracy and 31 were truely positive, 3 false positive, 8 truely negative and 1 false negative. The overall predictive accuracy was found in 39/43 cases (90.7%). Nineteen of the 43 patients (44.2%) with chemotherapy refractory cancers showed partial or complete remission under the guidance of SRCA result.