Cyclosporin A (CsA) is an immunosuppressive agent used in children for the treatment of steroid-dependent idiopathic nephrotic syndrome (INS). Despite its benefitial effect on a course of the disease CsA may exert nephrotoxic effects because of its vasoconstrictive properties. CsA-dependent disorders of the peripheral flow (Raynaud phenomenon--RP) have been recently described. The aim of the study was to assess the effect of CsA on the peripheral circulation. The study group comprised 16 children (12 male, 4 female; mean age 9.8 +/- 4.5 years) treated with CsA for at least 6 months due to INS (mean treatment time 39 +/- 27 months). Thirteen age- and sex-matched individuals served as controls. Peripheral circulation disorders were evaluated by means of a cold stress test (both hands were held in lukewarm water (20 degrees C) for 1 minute and thereafter the changes in the hand temperature were recorded with thermographic camera (Inframetrics SC1000). RP assessment was performed according to the method described by Ammer and Ring. The temperature gradient of 4 degrees C or greater maintained between metacarpal and peripheral areas of a hand after 10 minutes was considered diagnostic for RP. According to these criteria RP was confirmed in only 3 patients from the study group and in 2 controls. However, the time of the temperature increase in the first 5 minutes after cooling was considerably shorter in the children with INS (0.26 +/- 0.26 degrees C/min vs 0.51 +/- 0.29 degrees C/min, p=0.02). No correlation between CsA serum concentration, CsA dose and impairment of the hand temperature increase was found. The study confirmed that in children suffering from INS treated with CsA peripheral blood flow disorders can be seen. It seems that impaired vessel reactivity may result from the vasoconstrictive effect of CsA.