The Nb rat prostatic adenocarcinoma is a well-characterized, hormonally induced family of tumors that are all readily transplantable into congenitally athymic (nude) mice. Because of this versatile heterotransplantation model, multiple replicate copies of individual tumors can be studied "in rodent." We have extended this by studying the chemotherapeutic response of such tumors and believe that this provides a useful avenue for evaluation of cytotoxic agents. Indeed, this combination of both animal model systems may provide a useful experimental tool to evaluate tumor growth, histopathologic changes and responsiveness to appropriate therapy. We report herein that two Nb rat prostatic carcinomas (2 Pr-129-D-11A and Pr-90) and thie responsiveness to Adriamycin and 5-fluorouracil are objective by studying both growth rates and tumor histology.