Iron deficiency represents an important problem in peritoneal dialysis patients, especially during erythropoietin therapy. A combination of serum ferritin, transferrin saturation, and/or the percentage of hypochromic red cells should be used to assess iron status in peritoneal dialysis patients. Primarily, oral iron supplementation should be the preferred therapy. However, most of the studies using oral substitution in erythropoietin-treated peritoneal dialysis patients show a progressive decline of serum ferritin. Therefore, parenteral iron supplementation is required in part of the patients, and the intravenous route should be preferred in these cases. Intravenous iron therapy is recommended if serum ferritin falls below 100 microg/liter and should be stopped if the serum ferritin level is more than 650 microg/liter. The optimal form of intravenous iron supplementation is still unclear. Injections once to three times per week restrict the patients' flexibility, but application of higher doses in longer intervals may lead to an impairment of neutrophil functions, probably connected to a higher risk of infection. We treated 17 stable peritoneal dialysis patients with 100 or 200 mg iron saccharate monthly over a period of six months and found an increase of transferrin saturation (from 12.1+/-1.6 to 20.9+/-2.4%, P = 0.026), serum ferritin (from 100.4+/-32.0 to 372.4+/-54.6 microg/liter, NS) and hematocrit (from 32.0+/-0.8% to 35.1+/-0.9%, P = 0.099). The required erythropoietin dosage could be reduced significantly (from 148.4+/-30.3 to 69.4+/-19.5 U/kg/week, P = 0.025). Side effects occurred in 0.9% after application of 100 mg and in 5.9% after injection of 200 mg iron saccharate. The incidence of catheter infections and peritonitis was the same in the period before and after the start of treatment. Further studies are needed to find the most suitable regime of iron supplementation for peritoneal dialysis patients.