Danazol, an attenuated androgen, was given intermittently to three patients with hemophilia A. The rise in factor VIII activity with danazol treatment was associated with a fivefold decrease in hemorrhagic episodes and plasma concentrate product utilization when compared with similar periods without the drug. Four other patients with moderate hemophilia A who received danazol for 14 days had an increase of 400% to 850% in their factor VIII levels. Of four patients without detectable levels of factor VIII who were treated with danazol, two had elevations of the factor VIII level, to 3% and 4%, respectively. Danazol appears to be an effective treatment for patients with hemophilia A.