Data are presented on the response rates, maximum rate of cell kill, and survival rates for individual and groups of mice with MOPC 104E myeloma treated with a variety of chemotherapeutic agents and combination regimens used in clinical human myeloma. The tumor immunoglobulin M measurements are used to evaluate the therapeutic effects of drugs. Prednisolone and mescaline, when given as single drugs, showed no therapeutic action and the animals died of tumor as in the controls. The immunoglobulin M values are very similar and ranged between 8, 125 and 13, 410 μg/mouse. Prednisolone and melphalan given in combination indicated therapeutic effect. 1, 3-Bis(2-chloroethyl)-1-nitrosourea-cyclophosphamide-prednisolone combination caused tumor regression but was toxic as shown by the immunoglobulin M values and percentage of survival. The complications and potential uses of this system, which utilized only 40 animals in 64 days, are discussed. © 1975, American Association for Cancer Research. All rights reserved.