The predictive value of the subrenal capsule (SRC) assay for cancer chemotherapy was tested in five rat tumors. Tumor-bearing rats were used as controls. In order to simulate clinical chemotherapy, different dose regimens and drug combinations were used. All five tumors were evaluable in in the SRC assay. Taking into account cytotoxic drugs, 86% compatibility was obtained between the SRC assay and the rat model. Antitumor effect of three antiestrogenic compounds could not be predicted by the SRC assay. It is concluded that the SRC assay can be expected to have predictive value in the assessment of tumor sensitivity to single and combination chemotherapy based on experimental animal models.