Thirty unrelated Japanese adult patients with idiopathic membranous glomerulonephritis (IMG) and 50 unrelated Japanese normal controls were examined for HLA class II genes. Both the 3.0 kb DQB and the 6.2 kb DQA restriction fragments were simultaneously identified in 86.7% of the patients. These were significantly different from the 14% frequency of the fragments in controls (relative risk = 39.9; P = 1.7 x 10(-10)). The haplotype DR2-DQwl associated with IMG seemed to be Dw2 which was essentially different from the haplotype common to the normal Japanese population. Dw12. This was because most of the restriction fragment length polymorphism (RFLP) of DQB and DQA of the patients coincided with that of homozygous cell lines with Dw2. The DRB probe showed no significant differences in the hybridization patterns between the patient group and HLA-matched controls. These findings indicate that the specific HLA-DQ polymorphism correlates primarily with Japanese IMG.