Concentration of erythropoietin (Epo) and iron reserves (IR) belong to the essential factors determining erythropoiesis in haemodialysis patients. Patients on dialysis with acquired kidney disease (ACKD+) can control anaemia better than patients without acquired kidney disease (ACKD-). Therefore we decided to check if plasma Epo levels and IR differ significantly in both groups of patients. Forty chronically haemodialyzed patients after ultrasound diagnosis were divided into 18 patients (45%) with ACKD+ and 22 (55%) without ACKD-. In both groups of patients we compared their plasma levels of Epo and IR. Plasma erythropoietin and ferritin levels were measured by enzymatic immunoassay. Iron reserves were estimated by the formula: IR = 400 x [ln (ferritin)-ln (50)]. In the ACKD+ group 72% of patients and in the ACKD- group 32% of patients did not require rHu Epo therapy. Plasma levels of erythropoietin and iron reserves did not differ significantly between ACKD+ and ACKD- patients. There must be also other factors than erythropoietin levels and iron reserves regulating erythropoiesis in these patients.