The preservation residual renal function (RRF) is important for adequacy of peritoneal dialysis. Oxidative stress from intravenous (IV) iron has been shown to cause renal damage. The effect of IV iron on RRF has not been studied. Here, we report our experience during April 1999-March 2005 of the effect of IV iron on RRF. The study group included 24 patients (9 men, 15 women). The mean age of the group was 61 +/- 17.7 years. Diabetes mellitus and hypertension were the underlying cause of end-stage renal disease in 55% of the patients. We found serum creatinine, creatinine clearance, urea clearance, urine output, hemoglobin, transferrin saturation, and ferritin all to be statistically significantly different before and after administration of IV iron to the patients. However, the rate at which the glomerular filtration rate (GFR) declined over time did not change significantly when calculated for the period before and after the iron infusion, suggesting that the changes we observed after IV iron infusion were the result of the declining RRF--the rate of that decline being unaffected by the IV iron. Furthermore, the rate of GFR decline in this study was similar to that previously reported in our patients.