• Acetylcholine receptor antibody (AChR-ab) and IgG were studied in vivo and in vitro in a patient with myasthenia gravis, who was undergoing multiple leukoplasmaphereses. In this patient, leukoplasmapheresis accelerated production of AChR-ab and total IgG as would be expected if antibody acted through feedback as an inhibitor of its own synthesis. Cells capable of suppressing AChR-ab production were demonstrated before and after leukoplasmapheresis, indicating that AChR-ab production in this patient was not the result of detectable loss of suppressor-cell activity.