Peripheral mononuclear cells (MNC) of patients with autoimmune thyroid disease have been shown to proliferate when cultured with human thyroglobulin (hTg). In addition, such a phenomenon is apparent in a certain number of healthy individuals. In this study we have attempted to correlate hTg-induced MNC proliferation, occurrence of anti-hTg autoantibodies and HLA phenotype (including Class II DR and DQ loci) in a population of HLA-typed normal blood donors. Fourteen out of 56 subjects showed a significant MNC proliferation to hTg. Three of them had anti-hTg autoantibodies in the serum, while none of the hTg-unresponsive subjects showed such antibodies. No correlation with HLA phenotype (including Class II DR5 specificity, referred as associated with Hashimoto's thyroiditis, and DQ alleles) was observed.