A multivariate statistical analysis of levels of serum acetylcholine receptor antibody (AChR Ab) obtained from 197 patients with various clinical forms of myasthenia gravis (MG) was performed. Elevated AChR Ab levels are specific for MG, but normal AChR Ab levels do not rule out MG. Patients in remission or with purely ocular MG had the lowest incidence of elevation of serum AChR Ab levels, while patients with generalized, severe MG, particularly in the presence of thymoma, tended to have the greatest antibody elevations. Corticosteroids depressed AChR Ab levels, but thymectomy did not exert a consistent effect on antibody levels within a 24‐ to 30‐month postoperative period. The relatively low 55% positivity of antibody elevations in all 197 patients probably reflects the use of heterologous (rat) AChR.