Cyclophosphamide (Cytoxan) is a phosphamide ester of mechlorethamine. Preliminary studies of the drug showed it to be effective in animal and human tumors.1-3Dobson and Abele4have reported 4 patients with mycosis fungoides who had satisfactory remission of their disease after therapy with cyclophosphamide. To date we have completed observations of 11 patients treated with cyclophosphamide and here report our observations. All the patients had a diagnosis of mycosis fungoides made by both clinical and histological criteria, except for one patient whose diagnosis was lymphosarcoma. All the patients had cutaneous tumors or elevated plaques. White blood cell, platelet, and red blood cell counts were performed at least twice weekly, and photographs were taken before and after treatment. The patients received cyclophosphamide until leukopenia or thrombocytopenia developed. The medication was then stopped and restarted when the blood cell counts returned to normal. All patients developed leukopenia or thrombocytopenia at