An HLA-DX alpha gene polymorphism was analysed by Southern blotting in 49 British patients with Graves' disease and 61 control subjects. Two previously described allelic fragments of Taq I digested genomic DNA at 2.1 kb (U) and 1.9 kb (L) were found. The genotype frequencies for UU, UL and LL did not differ from the controls in Graves' disease, either for the whole groups or when subdivided into HLA-DR3-positive and -negative subjects. There was a significant association of the U allele with HLA-DR3 in both controls (P less than 0.05) and Graves' disease (P less than 0.025). The results indicate that DX alpha polymorphism is not primarily associated with Graves' disease. The findings differ from recent studies which showed that DX alpha polymorphisms may contribute to susceptibility in other DR3-associated autoimmune diseases.