Background.Concomitant iron supplementation is required in the great majority of erythropoietin (Epo)-treated patients with end-stage renal failure.Intravenous (i.v.) iron supplementation has been demonstrated to be superior to oral iron therapy in Epo-treated haemodialysis patients, but comparative data in iron-replete peritoneal dialysis (PD) patients are lacking.Methods.A 12-month, prospective, crossover trial comparing oral and i.v.iron supplementation was conducted in all Princess Alexandra Hospital PD patients who were on a stable dose of Epo, had no identifiable cause of impaired haemopoiesis other than uraemia, and had normal iron stores (transferrin saturation >20% and serum ferritin 100-500 mg/l).Patients received daily oral iron supplements (210 mg elemental iron per day) for 4 months followed by intermittent, outpatient i.v.iron infusions (200 mg every 2 months) for 4 months, followed by a further 4 months of oral iron.Haemoglobin levels and body iron stores were measured monthly.Results.Twenty-eight individuals were entered into the study and 16 patients completed 12 months of follow-up.Using repeated-measures analysis of variance, haemoglobin concentrations increased significantly during the i.v.phase (108 ± 3 to 114 ± 3 g/l)compared with each of the oral phases (109±3 to 108±3 g/l and 114±3 to 107±4 g/l, P<0.05).Similar patterns were seen for both percentage transferrin saturation (23.8±2.3 to 30.8±3.0%, 24.8±2.1 to 23.8 ± 2.3%, and 30.8 ± 3.0 to 26.8 ± 2.1%, respectively, P<0.05) and ferritin (385±47 to 544±103 mg/l, 317±46 to 385±47 mg/l, 544±103 to 463±50 mg/l,respectively, P=0.10).No significant changes in Epo dosages were observed throughout the study.I.v.iron supplementation was associated with a much lower incidence of gastrointestinal disturbances (11 vs 46%,P < 0.05), but exceeded the cost of oral iron treatment by 6.5-fold.Conclusions.Two-monthly i.v.iron infusions represent a practical alternative to oral iron and can be safely administered to PD patients in an outpatient setting.Compared with daily oral therapy, 2-monthly i.v.iron supplementation in PD patients was better tolerated and resulted in superior haemoglobin levels and body iron stores.