A case of acute myelomonocytic leukemia following cytotoxic therapy for an oat cell carcinoma of the lung in a 48-year-old man is reported. This case is characterized by a long phase of increasing macrocytosis during cyclophosphamide maintenance therapy. 15 other cases of secondary leukemia to lung cancer from the literature are reviewed. All patients received alkylating agents. Most patients showed peripheral blood changes more than 3 months before the onset of acute leukemia. All leukemia cases, except one, were nonlymphocytic with a high frequency of erythroleukemia. The development of acute leukemia seems to be linked with an unexpected good response to chemotherapy in advanced or poor histologic prognosis cancers. With therapeutic improvement in lung cancer, secondary leukemia could become a major hazard as in other cancers successfully treated with cytotoxic agents.