The aim of the study was to assess urinary transforming growth factor (TGF)-beta1 in children with steroid-dependent nephrotic syndrome (SDNS) treated with cyclosporine A (CyA) and ACE inhibitors (ACEI). The study involved 24 children (14 boys and 10 girls) with SDNS and signs of focal segmental glomerulosclerosis. The children were treated with prednisone, CyA, and ACEI. All children were examined four times: A during relapse of proteinuria, before treatment with CyA and ACEI, and B after 3 months, C 6 months, and D 12 months of treatment. The control group consisted of 20 healthy children of the same age. The urinary TGF-beta1 level was determined by ELISA (R and D Quantikine). The serum CyA level was measured by monoclonal antibody fluorescence polarization immunoassay. Prior to CyA treatment, the urinary TGF-beta1 level was the highest (135.61+/-38.31 pg/mg creatinine). During CyA treatment, TGF-beta1 was reduced to 117.96+/-81.57 after 3 months, to 80.26+/-49.52 after 6 months, and to 44.00+/-31.83 pg/mg creatinine after 12 months, but it was still higher than in the control group. At 3 months there was a positive linear correlation between urinary TGF-beta1 and proteinuria (r=0.654, P<0.01). These results indicate that the urinary TGF-beta1 level increases in proportion to proteinuria during relapse of NS. Treatment with CyA and ACEI also influences urinary TGF-beta1, which is still higher after 12 months of treatment than in healthy children.