During the course of the last 6 years, this laboratory unit has evaluated the Nb rat prostate adenocarcinoma model with respect to various chemotherapies. Heretofore, tumors were treated after they had been implanted in the subcutaneous space. The most active chemotherapeutic agents have been cyclophosphamide, adriamycin, and cis-platinum. Herein, we report our initial experience utilizing the subrenal capsular assay. The advantage of this system is that one is able to determine the effect of chemotherapy in a very short period of time, ie, 7 days. This may be a method to save considerable expense and may serve as a useful predictor for potential future chemotherapeutic trials. In our assay systems, cyclophosphamide, adriamycin, cis-platinum, and methotrexate did result in a significant decrease in the change in tumor volume. This change paralleled the results that we have seen in the past with the use of chemotherapy of the subcutaneous tumor nodules. Further exploration of this method is warranted from a time efficiency standpoint as well as a cost standpoint.