Leptin produced by fat cell has an unanticipated role in hematopoietic system development. We examined the relationships between leptinemia and requirements of erythropoietin (Epo), endogenous Epo levels as well as markers of inflammation: C-reactive protein, tumor necrosis factor α (TNFα) and interleukin-1 (IL-1) in rHuEPO-treated patients maintained on chronic hemodialyses or peritoneal dialyses. The studies were performed on 51 chronically hemodialyzed patients, 20 of them did not receive rHuEPO, 31 subjects received rHuEPO, and 22 patients on CAPD, 13 of them did not receive rHuEPO, 9 subjects were given rHuEPO. In hemodialyzed patients (Epo and Non-Epo group) leptin levels were significantly higher when compared to CAPD patients (Epo and Non-Epo group, respectively). Leptin in peritoneal fluid was significantly higher in the Non-Epo group. In ultrafiltrate, leptin levels were below the detection limit of 0.5 ng/ml. Epo levels in the HD + Epo group were significantly lower than in the HD + Non-Epo group and CAPD + Epo group. TNFα and IL-1 concentrations were significantly lower in both groups of CAPD patients when compared to respective HD groups. Treatment with rHuEPO resulted in nonsignificant decline in serum leptin (p = 0.07 in HD and p = 0.08 in CAPD) and significant leptin loss in peritoneal fluid. It may be of clinical relevance in dialyzed patients. In both groups of Epo-treated patients, positive physiological correlation between leptinemia and BMI disappeared. Leptin levels do not correlate with rHuEPO requirements and serum Epo in dialyzed patients.