A study was done to evaluate the relationship between Graves' disease and the HLA system in South African Blacks of Zulu descent. One hundred and three patients with Graves' disease and 1416 control subjects were typed for HLA A, B, and C antigens while HLA DR antigens were done on 63 of the former and 330 of the latter. There was a significant increase in the frequency of HLA DR3 in patients compared to control subjects (57.1% vs 36.1%; P corrected = 0.014). A relationship was also seen at the DR1 locus (14.3% vs 4.6%; P corrected = 0.023).