Cyclosporin A (CyA) was administered at the Clinic of Nephrology, CCS, in treatment of 8 patients with steroid-resistant nephrotic syndrome (NS) caused by focal segmental glomerulosclerosis (FSG), Cyclophosphamide (CP) treatment was attempted in 6 of these cases, but without success. Prior to the onset of CyA therapy, CP treatment was interrupted, and the dose of prednisone was reduced to 0.4 mg/kg/48 h. CyA was applied in the initial dose of 5 mg/kg/bw/24h, and then adjusted so that CyA blood level was 80-120 ng/ml. Although CyA treatment caused proteinuric decrease in most of the patients (from 12.1 g/24 h to 8.2 g/24 h), complete NS remission was achieved in only one patient, the same as the incomplete one. The female patient with a positive response to CyA treatment behaved as "CyA-dependent" and each discontinuation of CyA therapy soon led to recurrent NS. Insignificant CyA effect on NS or renal function was registered in 4 patients, and the therapy was interrupted in two cases due to renal function impairment. Apart from nephrotoxicity, other CyA side effects were absent.