An association between HLA-DR7 and the steroid sensitive idiopathic nephrotic syndrome in the children has already been reported. Immunogenetic data in the less frequent steroid resistant form of this disease have never been published. In this study, we analyse HLA-A, B and DR typing in 99 cases of nephrotic children divided in 72 with the steroid sensitive (SS) form and 27 with the steroid resistant (SR) syndrome, in comparison with those of 207 healthy controls; Bf allotypes were determined in 53 of the patients. The results show the increased frequency of DR7 in the SS syndrome (75% vs 30%, RR = 6.9, pc less than 10(-6), while the SR one is more associated to DR3 (52% vs 27%, RR = 3, p less than 0.004). In the SS patients, atopy is associated to DR7 (p less than 0.001), which is not the case in the SR group. Furthermore, a high relative risk is associated to the phenotype DR3/DR7 (30% vs 4%; RR = 9.3; pc less than 0.0004), for the SR disease; besides, this phenotype is associated to an early onset of the disease and to lesions of focal sclerosis. Thus a heterozygous effect in the SR form of idiopathic nephrotic syndrome of children has been demonstrated; the steroid sensitive and the steroid resistant forms of the disease seem to have different immunogenetic components.