The aim of this study was to assess the serum concentration of high-sensitivity C-reactive protein (hs-CRP) in children with nephrotic syndrome (NS) treated with prednisone and cyclosporine A (CyA). Patients were divided into three groups: (I) 20 NS children (aged 4-14 years) in relapse and examined twice, (A) before treatment and (B) after proteinuria regression (a 3-4 week course of prednisone therapy); (II) 20 children with steroid-dependent or steroid-resistant NS, treated with CyA, also examined twice, (D) before treatment with CyA, (E) 6 months after therapy. A control group (C) consisted of 20 healthy children. Serum hs-CRP level was determined by a nephelometric method with a Behring Nephelometer 100 Analyzer, Dade Behring. The results showed that median hs-CRP concentration was the highest in children with relapsing steroid-sensitive NS before treatment (IA). After proteinuria regression (IB), the hs-CRP level had decreased and did not differ from that of healthy controls (C) (P>0.05). In group II, before CyA administration (IID), the level of hs-CRP was normal, but it had increased after 6 months of treatment (IIE) up to a level six-times higher than that of the control group (P<0.01). We concluded that, in children with steroid-sensitive nephrotic syndrome in relapse, the serum hs-CRP level is increased but returns to normal after 3-4 weeks of glucocorticoid treatment. In children chronically treated with CyA due to NS, serum hs-CRP level increases significantly during the therapy.