Androgenic hormones have stimulated erythropoiesis in patients with breast cancer and those with refractory anemia, as well as in castrated and in normal experimental animals. Observation of this erythropoietic effect by several investigators has led to use of androgens in treatment of myelofibrosis. Six of 8 such patients treated by the author for prolonged periods with massive doses of androgenic hormone showed improvement. Two women, aged 55 and 75, and 1 man of 64 responded with increased hemoglobin, reticulocytosis, cessation of transfusion requirements, and hypercellular marrow. Three women, aged 56 to 62, required fewer or no transfusions and showed reticulocytosis. Corticosteroids were found to potentiate the effect in some instances. A prolonged remission persisted after cessation of androgen therapy in one case but could not be sustained. Therapeutic levels have in some cases led to polycythemia.