Therapeutic effectiveness of pretazettine (PTZ) has been demonstrated in the intraperitoneally (i.p.) implanted Lewis lung carcinoma (LLC) in both syngeneic and allogeneic mice. The i.p. implanted LLC has been found to be sensitive to most standard drugs tested such as cyclophosphamide (CY), actinomycin D, 5-fluorouracil, methotrexate, 6-thioguanine and vincristine, in comparison to the subcutaneously (s.c.) or intravenously (i.v.) implanted LLC which was reported to be resistant to most standard drugs (s.c.-LLC) or resistant to actinomycin D, methotrexate and vincristine (i.v.-LLC). The effectiveness of PTZ was comparable to that of standard drugs in the i.p. implanted LLC system, and the combination therapy of PTZ with these standard drugs except vincristine was synergistically or additively effective. Also, the PTZ combination rescued the allogeneic mice from the risk of adverse (tumor-enhancing) effects of CY at moderate doses (25–50 mg/kg) given therapeutically.