Background: Intravenous (i.v.) ascorbic acid (AA) improves anaemia in iron-overloaded, erythropoietin (rEPO) hyporesponsive haemodialysis patients. While oral AA is readily attainable, the efficacy and safety of oral versus i.v. AA has not been examined.Methods: We conducted an open-label randomised parallel study on the effects of 8 weeks of 250 mg oral AA (n = 10) compared with 250 mg i.v. AA (n = 11) 3x/week on haemoglobin (Hb), ferritin and rEPO dose in 21 iron-overloaded haemodialysis patients. We also examined the effect of 3 months of 500 mg oral AA 3x/week (n = 70) compared with no treatment (n = 83) on Hb, ferritin and rEPO dose in 153 haemodialysis patients.Results: Patients had severe AA deficiency (mean 2.2 +/- SE 0.4 mg/L; normal range, 4.0-14.0). Following treatment, the plasma AA level increased (P <0.001), but was not significantly different between the groups. There was no change in Hb, iron availability and rEPO dose with oral or i.v. AA. There was a significant increase in serum oxalate but no significant changes in left ventricular function or renal calculi formation. In the second study, oral AA had no effect on Hb, rEPO dose and ferritin in the whole group and a subgroup of 30 with anaemia.Conclusion: Haemoglobin and iron availability did not improve following oral or i.v. AA in this select small group of iron-overloaded haemodialysis patients or in a larger population of haemodialysis patients given oral AA at a higher dose and for a longer duration. AA supplementation may still be warranted in view of severe AA deficiency in haemodialysis patients.