Data from 10 Chinese families in Hong Kong with multiple cases of thyrotoxic Graves' disease were analysed to determine whether genes predisposing to Graves' disease are linked to the HLA region. No evidence was obtained in favour of either dominant or recessive inheritance of HLA-linked susceptibility to Graves' disease. Six of 10 affected parent-offspring combinations had haplotypes containing HLA Bw46 which is more than would be expected from the antigen frequency of Bw46 in normal controls. It is concluded that HLA-associated genes play a role in determining disease susceptibility but that other factors are involved in determining disease expression.