Cyclosporine A (CsA) treatment was evaluated in 52 patients with severe generalized myasthenia gravis (MG) whose illness was not controlled by anticholinesterase drugs, thymectomy, corticosteroids, and azathioprine. The efficacy of CsA treatment was expressed by mean disability score quotient (MDSQ), which was obtained by comparing mean disability score (MDS) at the beginning of the treatment with the MDS at the end of the follow-up period. For the entire group of patients MDSQ was 53.3%, indicating moderate improvement. Analyzing individual cases, eight patients (15%) did not improve, 17 (33%) showed moderate improvement, 20 (38%) showed remarkable improvement, and seven patients (14%) achieved complete remission. The most common side effects were rise of serum creatinine (seven), hypertension (two), gingival hyperplasia (two), hypertrichosis (six), myalgia (10), and 'flu-like' symptoms (10 patients). The results of this study suggest that CsA is efficacious and safe treatment in severe and resistant forms of MG.