To evaluate angiotensin-converting enzyme (ACE) gene insertion/deletion polymorphism in nephrotic syndrome, 50 patients (minimal-change nephrotic syndrome, MCNS: 32 cases; focal segmental glomerulosclerosis, FSGS: 18 cases) and 50 control healthy subjects were examined. Their age ranged from 4-12 years. The distribution of ACE genotype was II 12%, ID 16% and DD 72 %. The control group had almost similar allelic distribution. However, the distribution of ACE genotypes in FSGS was different from those of MCNS. The DD genotype was more frequent in FSGS than the II genotype with (p<0.05). Patients with the DD genotype present more severe clinical manifestations and earlier age of onset. They also showed a lower responsiveness to corticosteroid therapy than those with other genotypes. Our results indicate that the ACE DD genotype in FSGS may be a risk factor for the poor responsiveness to steroid therapy and the more severe clinical manifestations. Also, DD genotype may be responsible for transformation of MCNS to FSGS.