Between 1976 and 1981, one of the authors operated on 16 patients for myasthenia gravis. Plasmapheresis was carried out preoperatively on seven patients, while nine patients were operated upon without previous plasmapheresis. The seven patients who underwent plasmapheresis had a smooth course pre- and postoperatively. In the other group, there were two postoperative myasthenic complications. Both patients improved with medication and plasmapheresis. Also, the degree of myasthenia gravis was slightly more severe in this group. From their experience, the authors conclude that plasmapheresis is a worthwhile and safe adjuvant in the preparation of myasthenic patients for thymectomy, especially those in Osserman class IV.