It is widely accepted that a long-term, alternate-day administration of adrenal corticosteroids after thymectomy is one of the most effective treatments of myasthenia gravis. However, some patients with myasthenia gravis show a tendency to develop steroid dependency, and require extremely prolonged administration of fairly high doses of steroids. Various types of adverse reactions to steroids are likely to occur in such cases. To avoid this, intermittent, single-dose administration of steroids was performed on a trial basis in the present study. Prednisolone, in doses of 50-100 mg, was given once every 3-7 days in three steroid-dependent myasthenic patients, in one case for up to 6 years. The effects of the intermittent treatment were as good as, and adverse effects less frequently found than in single-dose, alternate-day administration.