en Internal Medicine Internal Medicine Original Research Original Research Serum erythropoietin (EPO) concentration was measured by an enzyme-linked immunosorbent assay (ELISA) in 31 cases of chronic renal failure (CRF), including 20 hemodialysis (HD) patients, and compared with that of 31 healthy normal controls. Each patient served as a self-control comparing his or her pretreatment level with post-treatment values. There was a significant negative correlation between serum EPO and serum iron ( SI) concentration in HD patients (p<0.05) the correlation was more prominent after three months of hemodialysis (p<0.00l). The mean hemoglobin (Hb) concentration was significantly higher in patients who underwent HD more than once per week as compared with those who received HD once a week (p<0.00 1). In addition, patients on three months of HD had a higher Hb level as compared to those who had received HD for one month (p<0.001). Moreover, there was also a significant negative correlation between serum EPO concentration and dialysis adequacy (p<0.05), indicating that the erythropoietin-hematocrit feedback inhibition mechanism had improved due to general improvement of the patients' metabolism and possible removal of dialyzable toxins. Erythropoietin, anemia, chronic renal failure, hemodialysis. 299 302 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-330&slc_lang=en&sid=1 P KHAJEHDEHI 20031947532846005000 20031947532846005000 Yes From the Division of Nephrology, Department of Internal Medicine, School of Medicine, MA GHALAMBOR 20031947532846005001 20031947532846005001 No the School of Paramedical Sciences, Shiraz University of Medical Sciences, Shiraz, Islamic Republic of Iran.