Circulating IgG, IgA, and IgM antibodies to human eye muscle cytosol antigens were studied in 60 patients with Graves' ophthalmopathy using the indirect ELISA method. There was a significant difference in the levels of both IgG and IgA antibodies between the patients with Graves' ophthalmopathy and a control group (p < 0.001). IgA antibodies to eye muscle cytosol antigens were raised in 20 out of 29 patients with proptosis (class 3 ophthalmopathy), in comparison with 31 patients out of the total group of 60 with Graves' ophthalmopathy (p < 0.02). Anti-TSH receptor antibodies (TRAK) were not present in over half of the 31 patients with raised IgA antibodies to eye muscle antigens. However, a significant difference was found between the levels of IgG and IgA antibodies in the TRAK-negative patients (p < 0.05). These findings suggests that both IgG and IgA antibodies to eye muscle antigens might be important in the development of ophthalmopathy.