We have investigated whether plasma exchange in myasthenia gravis synergises with additional immunosuppressive drug therapy (azathioprine, cyclophosphamide or cytosine arabinoside). Serum anti-acetylcholine receptor (AChR) antibody titres were followed over 28 days after a course of PE in 20 patients, of whom 17 were taking 20-80 mg prednisone on alternate days. No significant difference was ob...