Because a 72 kilodalton heat shock protein (HSP 72) is associated with autoimmune thyroid disease and is selectively expressed in fibroblasts derived from involved sites of patients with Graves' ophthalmopathy and pretibial myxedema, we studied the influence of oxygen free radicals (OFR), oxygen radical scavangers (ORS), and antithyroid drugs on HSP 72 expression in Graves' retroocular fibroblasts.