Myasthenia gravis (MG), the most common neuromuscular transmission disorder, is an antibody-mediated autoimmune disease that stems from a loss of acetylcholine receptors (AChR) at neuromuscular junctions. AChR autoantibodies are diagnostic of MG, and are found in 85-90% of MG patients. AChR binding autoantibodies are present most frequently in MG and provide the most reliable information for diagnostic screening. A small portion of patients with early onset or ocular restricted MG may only have AChR modulating autoantibodies, thus if AChR binding autoantibodies are absent in a patient with weakness or ocular symptoms consistent with MG, AChR modulating autoantibodies should be ordered. AChR blocking autoantibodies are directed against the neurotransmitter-binding site and may be the only AChR autoantibody in about 1% of MG patients.