Danazol, an attenuated androgen developed for the treatment of endometriosis, has recently been found useful in the treatment of several hematologic disorders, including idiopathic thrombocytopenic purpura (ITP), autoimmune hemolytic anemia (AIHA), paroxysmal nocturnal hemoglobinuria, myelodysplastic syndrome, and others. Our studies of the past 6 years have demonstrated that danazol is advantageous in the treatment of AIHA, and in specifically defined populations of ITP patients. Of 96 ITP patients treated with danazol 61% overall had excellent/good responses, but this rate varied markedly with prognostic factors, e.g. 82% in older women versus only 18% in younger women. Of 28 AIHA patients, 77% with idiopathic type and 60% with secondary type were excellent/good responders. When the drug was discontinued after 1 year or more of therapy, lasting unmaintained remissions of up to 5 years were often observed in both ITP and AIHA, a notably important benefit. The side-effects of danazol are generally much less serious than with glucocorticoids. Glucocorticoids can be tapered off and in most cases discontinued completely with danazol therapy in AIHA and chronic ITP. Approximately one third of ITP patients who failed on glucocorticoids are successfully maintained on danazol. Its mechanism of action in these disorders is currently under study in our laboratory, stimulated by new findings. Tentatively, danazol appears to modify cell membranes in a manner leading to specific immune modulations, as discussed. Further study is warranted to explore its application to other autoimmune and membrane-related disorders, and to clarify its mechanism of therapy.