Fourteen patients (twelve of them were women) with severe myasthenia gravis who had not responded to any treatment at all, were treated by cytostatic drugs. Both azathioprine and cyclophosphamide single or in combination are used. All patients except two were thymectomized and almost all were treated by plasmapheresis and corticosteroid before and during the cytostatic treatment. All patients take cholinesterase inhibitors. No serious complications were observed. The patients received 100-200mg of azathioprine and/or 100-200mg of cyclophosphamide daily by oral route, the first during 20 months and the second one during 6 months. Three patients received cyclophosphamide lg daily by venous rute during 6 months at 15-20 days intervals. The preliminary results were favourable occurring important improvement in 71.4% of the cases. Their performance increased considerably. The progress of the disease was generaly stabilized. Exacerbations and crises did not reccur, except in one case. Only three patients had not responded to the treatment, one responded poorly but better later and one had an exacerbation after the 24º month. This patient returned to azathioprine.