An association of human leukocyte antigens (HLA) with idiopathic nephrotic syndrome (INS) in childhood was studied to characterize the immunogenetic background. We determined the class I antigens using the microlymphocytotoxicity test as well as class II antigens (DRB, DQB, DQA) and class III antigen (complement 4) using DNA restriction fragment length polymorphism (RFLP) in 36 children with INS. In the current study, neither the single allele in HLA class I antigen nor the single gene frequency in the class II region was significantly increased, in contrast to the results in Caucasian INS patients in whom a genetic predisposition to the HLA system, especially to HLA B8, DR3, and DR7, has been frequently reported. Also, in our data, the frequency of deletion of complement 4 gene was not different from that of the controls. These data suggest that there is a difference in immunogenetic background between Caucasian and Japanese INS patients as far as HLA is concerned.