BACKGROUND: Preliminary clinical evidence suggests that heme iron polypeptide (HIP) might represent a promising, novel oral iron supplementation strategy in chronic kidney disease. The aim of this multi-centre randomized controlled trial was to determine the ability of HIP administration to augment iron stores in darbepoetin (DPO)-treated patients compared with conventional oral iron supplementation. METHODS: Adult peritoneal dialysis (PD) patients treated with DPO were randomized 1:1 to receive two capsules daily of either HIP or ferrous sulphate per os for 6 months. The primary outcome measure was transferrin saturation (TSAT). Secondary outcomes comprised serum ferritin, haemoglobin, DPO dose and responsiveness, and adverse events. RESULTS: Sixty-two patients were randomized to HIP (n = 32) or ferrous sulphate (n = 30). On intention-to-treat analysis, the median (inter-quartile range) TSAT was 22% (16-29) in the HIP group compared with 20% (17-26) in controls (P = 0.65). HIP treatment was not significantly associated with TSAT at 6 months on multivariable analysis (P = 0.95). Similar results were found on per-protocol analysis and subgroup analysis in iron-deficient patients. Serum ferritin levels at 6 months were significantly lower in the HIP group (P = 0.003), while the cost of HIP was 7-fold higher than that of ferrous sulphate. No other differences in secondary outcomes were observed. CONCLUSIONS: HIP showed no clear safety or efficacy benefit in PD patients compared with conventional oral iron supplements. The reduction in serum ferritin levels and high costs associated with HIP therapy suggest that this agent is unlikely to have a significant role in iron supplementation in PD patients.