SummaryFifty cases of malignancy have been treated with cyclophosphamide alone or in combination with Rôntgen therapy. Palliative results, sometimes dramatic, were achieved in some cases. Good results were obtained in the management of lung carcinoma with the association of cyclophosphamide and X-ray therapy. A special study of the leukocytic reaction is reported . It is concluded that cyclophosphamide is an effective drug, of moderate toxicity, and easy to use.