An IgG autoantibody that binds to the thyroid-stimulating hormoneceptor, stimulating the excessive production of thyroid hormones and causing hyperthyroidism. This immunoglobulin is found in the blood of about 75% of patients with Graves’ disease but is used rarely for diagnostic purposes, because the diagnosis usually can be established on clinical grounds, i.e., on finding a patient with hyperthyroidism with a diffuse, nontender goiter, exophthalmos, and/or pretibial myxedema.