Iron balance is critical for adequate erythropoiesis in hemodialysis patients treated with recombinant human erythropoietin (EPO). The role of oral iron therapy in maintaining or replenishing iron stores has not yet been well defined in such patients. We undertook a double-blind, placebo-controlled study to evaluate the efficacy of oral iron in 49 hemodialysis patients, divided into two groups, based on adequate or deficient iron stores. These groups were treated for 3 months with 150 mg elemental iron (Polysaccharide complex, Central Pharmaceuticals) or placebo, twice daily. Laboratory parameters were followed for five months. These parameters included: hematocrit (Hct), ferritin, transferrin saturation (Tsat), and zinc protoporphyrin (ZPP). A side-effects questionnaire was recorded monthly. Our results indicate that iron replete patients show evidence of falling iron stores during the study period; this observation was identical in both oral iron and placebo subgroups. Iron deficient patients had a significantly greater drop-out rate due to side effects when compared to iron replete patients (33% vs. 8%), despite equivalent responses to the side-effect questionnaire. We conclude: 1) Oral iron fails to maintain iron stores in iron replete patients; 2) Iron deficiency observed in this study may be due to poor medication compliance rather than side-effects.