HLA-A and B-antigens were tested by a standard microlymphocytotoxicity technique in 126 controls and 225 thyrotoxic patients of Greek origin [173 with Graves' disease and 52 with toxic nodular goiter (TNG)]. We found: i) an increased frequency of HLA-B8 (21.4% versus 7.1%) and a decreased frequency of HLA-B12 (2.9% versus 18.2%) in Graves' disease when compared with controls; ii) no differences in the distribution of HLA-A, -B antigens in TNG, when compared with either controls or Graves' disease. These findings suggest that the associations between HLA-A, -B antigens and Graves' disease in Greek patients are similar to those reported in other caucasians. The absence of any correlation between HLA-A, -B and TNG provides additional laboratory evidence that TNG and Graves' disease represent different entities.