It is well known that circulating antibodies are produced by plasma cells derived from B lymphocytes, and T lyphocytes are endowded with the capacity to regulate the type and intensity of virtually all immune responses. Therefore, the measurement of relative and absolute number of lymphocytes in the peripheral blood of myasthenia gravis patients could be of value. We have studied the distribution pattern of lymphocytes and helper/suppressor ratio in the peripheral blood of 28 myasthenic patients in comparison with 10 patients of other neurologic diseases as control by using immunobead method. There was no significant differences between 17 myasthenic patients who had taken only anticholinesterase and control. But in 17 patients who had taken steroid, Helper T lymphocyte was decreased significantly compared to control. Both T lymphocyte and B lymphocyte were also decreased significantly compared to 17 myasthenic patients who had taken only anticholinesterase without steroid therapy. In 3 patients who had undergone thymectomy, there was significant decreases of suppressor T lymphocyte. Plasma exhange as a treatment for myasthenia gravis is currently the subject of clinical interest and research. Clinical response and muscle power measured by using sphygmomanometer were followed in 2 patients in myasthenic crisis and in 4 patients with severe disease refractory to all other treatment modalities, received 4-6 cycles of plasma exchange with Hemonetics 30-S. 2 patients had a recurrence 1.5 and 6 months after first course of plasma exchange respectively, Therefore, they had to take a second course of plasma exchange. The satisfactory increment of muscle power was noticed in 5 out of 6 cases after fourth plasma exchange.