Plasmapheresis plays an important role in the acute management of patients with severe myasthenia gravis. Although plasmapheresis is now in use for more than 20 years, some controversies remain about the indication and the place in the therapy. It is generally found that the effect starts one week after the start of PP and lasts about 2-4 weeks after the last exchange; because of this temporary effect use of concomitant immunosuppressive medication is recommended. Compilation of data from 13 large series shows that about 75% of the patients react favourably. The relation between fluctuations of antibodies and the effect of PP is poor; even seronegative patients may improve as well.