We tested sera and purified immunoglobulin (Ig) fractions from patients with autoimmune thyroid disorders (AITD), with and without ophthalmopathy, and normal subjects, for the presence of antibodies reactive with eye muscle membrane antigens in an optimized enzyme-linked immunosorbent assay (ELISA). We found no correlation between ELISA results and the presence or severity of ophthalmopathy in patients with AITD for either serum or Ig, and there were no significant differences between the mean values (±SE) for the three groups (AITD with ophthalmopathy, AITD without ophthalmopathy and normals) for either serum or Ig. In contrast Ig from 8 of 19 (45%) patients with thyroid-associated ophthalmopathy reacted with a 64 kDa eye muscle membrane antigen in SDS-polyacrylamide gel elec-tropohoresis and Western blotting, while tests were positive in only one of the 8 patients with AITD without eye disease and in none of the 8 normal subjects. The presence of antibodies to a 64kDa antigen in immunoblotting did not correlate with the levels of antibodies measured in ELISA. We conclude that the ELISA, incorporating crude membrane fractions as antigen, is not useful as a clinical test for eye muscle autoantibodies.