The presence of HLA antigens B8 and DR3 in an individual is associated with his predisposition to developing Basedow's disease. A comparative study of a clinical course and immunological characterization of this disease in 208 patients, divided with relation to the presence or absence of the above antigens, showed that the disease developed in patients with HLA B8 and DR3 at a younger age and was accompanied twice as more frequently by ophthalmopathy. Thyrotoxicosis relapsed among these patients in conservative therapy much more frequently. A relapse after surgical intervention in the study group was noted thrice as more frequently compared to the control group. Focal infiltration of thyroid tissue with lymphoid cells was determined twice as less frequently in patients with HLA B8 and DR3. Any statistically significant difference was unnoticed in the severity of thyrotoxicosis and the frequency of detection of antibodies to thyroglobulin.