Using a combination of polymerase chain reaction amplification, oligonucleotide mismatch hybridization, and direct sequencing, we analyzed the distribution of a recently described TSH receptor gene polymorphism in 88 patients with Graves' disease but no clinically apparent eye disease, 53 patients with Graves' disease and associated ophthalmopathy, 39 patients with autoimmune hypothyroidism, and 156 control subjects. No significant difference in the distribution of this polymorphism was found between either group of Graves' patients, the hypothyroid patients, or the control group. These results suggest that this coding region polymorphism is not associated with the occurrence of Graves' disease or Graves' ophthalmopathy.