A sodium-proton exchanger (NHE) is a membrane transport system taking part in intracellular sodium homeostasis. An increased NHE activity was observed in erythrocytes of primary hypertension (NTP) patients. The clinical use of cyclosporine A has provided new perspectives in organ transplantation and in the treatment of autoimmune diseases but is accompanied by side effects like hypertension. Study group consisted of 40 patients with end stage renal failure (ESRF) before and after renal transplantation and 48 controls. The activity of NHE was significantly higher after transplantation than before renal transplantation (p = 0.05) and than control group (p = 0.05). There was positive correlation between NHE activity and cyclosporins blood level. We excluded (in vitro and in vivo study) the influence of uremic toxins on NHE activity in patients with ESRF before renal transplantation. It gave opportunity to compare the activity of NHE before and after renal transplantation according only to aspect of immunosuppressive treatment.