The localization and functional characteristics of tumor necrosis factor(TNF) beta gene raise the possibility that it may be involved in the susceptibility to autoimmune thyroid diseases. To investigate whether a TNF beta gene polymorphism is associated with autoimmune thyroiditis, we analyzed the TNF beta gene polymorphism with the restriction enzyme NcoI in 48 Korean patients with atrophic autoimmune thyroiditis [23 were found to be thyrotropin binding inhibitor immunoglobulin(TBII) positive, 25 TBII negative], 52 goitrous autoimmune thyroiditis, and 129 healthy controls. Two TNF beta alleles were identified from the restriction fragment length polymorphism studies of amplified genomic DNA. In atrophic autoimmune thyroiditis patients positive for TBII, 7 of 23 patients were homozygous for the TNF beta * 1 allele, 3 were homozygous for the TNF beta * 2 allele, and 13 were TNF beta * 1/2 heterozygous compared to controls(P = 0.20). Also, there were no associations between the TNF beta gene polymorphism and either TBII-negative atrophic autoimmune thyroiditis or goitrous autoimmune thyroiditis. Of the HLA-class II antigens, the frequency of HLA-DR8 was significantly greater among the 23 Korean patients with TBII-positive atrophic autoimmune thyroiditis compared to control subjects (Pc = 0.003). When the HLA-DR8 positive patients with TBII-positive atrophic autoimmune thyroiditis and controls were analyzed separately, the DR8 positive patients with TBII-positive atrophic autoimmune thyroiditis had more homozygotes for the TNF beta * 1 allele(6/12, 50.0%) and no homozygotes for the TNF beta * 2 allele, as compared to the DR8 negative patients with TBII-positive atrophic autoimmune thyroiditis and DR8 positive controls(P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)