This paper reports a study on the treatment of predialysis patients with recombinant human erythropoietin (r-HuEPO). The haematocrit, haemoglobin, reticulocyte and platelet values as well as creatinine and creatinine clearance evaluated by standard and radio-isotopic methods before, during and after r-HuEPO treatment were determined. The slope of the inverse creatinine versus time curves was studied too. The authors did not observe any variation of the renal function parameters during and after study and suggest their protocol of r-HuEPO administration for predialysis patients.