The paper is concerned with the determination of class I antigens of the HLA system in 104 patients with diffuse toxic goiter and in 643 donors. A study was made of the distribution of antigens, haplotypes and phenotypes of the HLA system. An increase in the frequency of antigens A28 and B8, haplotype [correction of haploptin] A1-B8 and phenotype B7, B8 and a decrease in the frequency of antigens B13, B17 and Cw4 were revealed. Immunogenetic indices showed no correlation with clinical, hormonal and immunological manifestations of the disease, neither did they influence the therapeutic prognosis of diffuse toxic goiter. A great genetic difference was revealed between patients with a relapse (decompensation) and those at remission.