Corticosteroids have been useful in the management of myasthenia gravis (MG), but their efficacy has been limited by the slow onset of improvement, initial worsening of MG, refractoriness of some patients, and side effects of large daily doses. High-dose intravenous methylprednisolone pulses have been reported to produce rapid improvement in several immunologic disorders. In this study we administered 2 g of methylprednisolone intravenously every five days to 15 consecutive patients who had exacerbation of generalized MG. Satisfactory improvement occurred in ten of 15 patients after two courses and in two of five patients after a third course. Onset of improvement began a mean (+/- SD) of 3 +/- 1.1 days after the first infusion, 2.1 +/- 1 days after the second, and 2.4 +/- 1 days after the third, and reached its maximum level 8.9 +/- 6.1 days after the last infusion. A decrease in strength occurred in three patients 1.43 +/- 1.30 days after each infusion, was not marked, and lasted three days, following which improvement generally occurred. Side effects were minimal. After improvement, a daily dose of prednisone (30 mg) was used to maintain improvement. Use of pulse therapy at five-day intervals for the management of severe MG seems to have an advantage in that it produces less initial worsening and more rapid improvement in MG, enabling smaller daily maintenance doses to be employed, with fewer side effects.