The non-tumorigenic cells of X63-Ag8.653 mouse plasmocytoma line transfected with murine interleukin 2 cDNA (X63-mIL-2) served us as the source of the cytokine to induce or to augment antitumor response in syngeneic BALB/c or semisyngeneic (CD2F1) mice challenged subcutaneously with either "wild" line tumor cells (X63/0) or with non-related methylcholantrene induced BFS1 fibrosarcoma of BALB/c mice. When applied peritumorally in several injections (2 to 6) to mice with non-advanced stages of the tumors, IL-2-secreting cells were able to cause tumor growth retardation in most of the treated mice and to induce tumor rejection in some of them. The combination chemoimmunotherapy was attempted in mice with advanced BFS1 fibrosarcoma using compound CBM-4A (the bromoanalog of ifosfamide) administered at various time (4 h or 3, 5 or 7 days) before the first of two local injections of transfected cells. The strategy proved to be more efficient in the tumor growth inhibition as compared with the cytostatic alone.