It is now recognized that the majority of patients on epoetin therapy require intravenous (IV) iron supplementation to maximize the response to treatment. Of the IV iron preparations available, iron sucrose has proved its efficacy and safety; however, there are no guidelines or systematic studies examining the optimum safe dosage regimen for this compound. The aim of the present study was to investigate prospectively a variety of dosing regimens for IV iron sucrose in patients with renal failure to develop treatment strategies for this preparation. A total of 335 iron infusions was administered to 249 patients in this study, which was conducted in four phases. In phase I, 89 patients were administered a dose of 200 mg as an IV infusion over 2 hours. No adverse events were seen. A 500-mg dose by 2-hour infusion was then assessed, but was abandoned after 8 of 22 patients developed reactions characterized by dizziness, hypotension, and nausea. The dose was then reduced to 300 mg by 2-hour infusion for the next 189 patients, and again, no adverse reactions were witnessed. Finally, a 400-mg dose by 2-hour infusion was examined in 35 patients, but 2 patients experienced such symptoms as hypotension, nausea, and lower back pain. Both the 200- and 300-mg doses of IV iron sucrose administered over 2 hours appear to be safe. The incidence of adverse events with the 400- and 500-mg doses administered as a 2-hour infusion seems too high to recommend their routine use, although it may be possible to administer these doses over a longer period.