This article describes the pharmacokinetics, pharmacodynamics of darbepoetin alfa, a novel erythropoietin analogue showing a long-lasting effect. In the single-dose segment of this study, hemodialysis patients were administered darbepoetin alfa intravenously in increasing doses ranging from 90-180 μg/body. In the repeated-dose segment, switching to once-weekly administration of darbepoetin alfa was attempted in 14 patients who had been receiving intravenous rHuEPO two or three times a week. The intravenous dose of darbepoetin alfa to be administered once weekly (10-60 μg/body) was titrated to maintain hemoglobin levels within±1.0 g/dL of the individual mean baseline level as well as in the range of 9-12 g/dL for 28 weeks. When given as a single dose, darbepoetin alfa showed almost linear pharmacokinetics within the dose range of 90-180 μg, and the mean elimination half-life ranged from 45.37 to 48.67 hours and the total body clearance ranged from 52.69 to 64.07 mL/hour/body. When given as repeated doses for up to 28 weeks, almost no changes were observed in the pharmacokinetics of darbepoetin alfa, i.e., the mean elimination half-life and total body clearance rate were 33.14 hours and 76.90 mL/hour/body at Week 1, 39.13 hours and 83.89 mL/hour/body at Week 21, and 42.09 hours and 83.48 mL/hour/body at Week 28. darbepoetin alfa was well tolerated and no antibodies against it were detected. The results suggest that less frequent intravenous administration of darbepoetin alfa can effectively maintain target hemoglobin levels safely in the treatment of renal anemia in hemodialysis patients.