Cyclophosphamide was given intermittently rather than daily to 14 patients with autoimmune thrombocytopenic purpura. Eight patients responded and six did not. In those who responded the rise in platelet count was rapid, and in all patients the lack of toxicity was striking. Intermittent cyclophosphamide seems effective in some cases of autoimmune thrombocytopenia and is safe, at least in the short term. Controlled trials would be required to prove that intermittent is better than daily administration.