Based on characteristic features of the toxic effect of chemotherapeutic drugs, these were selected for chemotherapy of experimental tumors. The reliable results were obtained in three variants of combinations. 1) A combined administration of drugs active with respect to one and the same tumor but which toxic effect do not coincide. 2) Simultaneous administration of two drugs in doses tolerable for gaining a therapeutic effect, obtained in their separate use in massive doses, but with a less toxic damage to the body. 3) A combination of substances possessing a selective toxic action on the tissue bearing the tumor under treatment.