The nude mouse was used to evaluate transplantation of feline tumors and subsequent doxorubicin chemotherapy. Three mammary gland adenocarcinomas and one salivary gland adnoecarcinoma were readily transplanted. All were successfully passed at least once. The two sarcomas, a fibrosarcoma and a malignant hemangioendothelioma, failed to grow when transplanted. Growth rates for the adenocarcinomas appeared to be specific for individual tumors. Generally, tumor weights increased five to eight times by days 40 to 50. Structural changes were not observed histopathologically in tumors transplanted several times. When doxorubicin was given intraperitoneally (1 mg/kg of body weight) weekly for 6 weeks to nude mice with transplanted feline mammary gland adenocarcinoma, there was no significant difference (P less than 0.05) in weights of tumors of experimental (n = 150 and control (n = 10) mice.