Anti-idiotype sera, raised in rabbits against anti-acetylcholine receptor (AChR) (idiotype) purified from the serum of three myasthenia gravis patients, inhibited binding of homologous idiotype to the AChR by up to 80%. The expression of idiotype in the three individuals changed very little over a period of several years, during which they showed a declining trend in overall anti-AChR antibody. Only one of the four anti-idiotype sera inhibited the binding of anti-AChR from a number of other patients. Our results indicate a consistency of idiotype expression within an individual, and fail to show substantial idiotype sharing between individuals.