Although danazol is effective in the treatment of idiopathic thrombocytopenic purpura, its long-term safety and optimal dosage are not well established. We compared low (50 mg/d) and conventional (400 to 800 mg/d) dosages in 24 patients. Thirteen patients received the low dose 1 to 24 months after conventional doses had been discontinued (group 1). Five patients received low doses immediately after the conventional doses (group 2). Six patients were treated with low doses from the outset (group 3). In group 1, similar responses to either dose were seen in 9 patients, whereas there were better responses to conventional doses in 3 and to the lower dose in 1. All patients in group 2 maintained remissions with low doses. There were two excellent-good responses, one fair, and three poor responses in group 3. Side effects were generally less frequent and severe with the low doses. Low-dose danazol is better tolerated but took longer to obtain remissions, and is useful for maintenance therapy in the management of idiopathic thrombocytopenic purpura.