Darbepoetin alfa is a novel erythropoiesis-stimulating protein with a two- to threefold longer half-life than recombinant human erythropoietin (epoetin) in adult patients with chronic kidney disease (CKD). This randomized, open-label, crossover study was conducted to determine the pharmacokinetic profile of darbepoetin alfa in pediatric patients with CKD. Twelve patients 3-16 years of age with CKD were randomized and received a single 0.5 micro g/kg dose of darbepoetin alfa administered intravenously (IV) or subcutaneously (SC). After a 14- to 16-day washout period, patients received an identical dose of darbepoetin alfa by the alternate route. After IV administration, the mean clearance of darbepoetin alfa was 2.3 ml/h per kg, with a mean terminal half-life of 22.1 h. After SC administration, absorption was rate limiting, with a mean terminal half-life of 42.8 h and a mean bioavailability of 54%. Comparison of these results with those from a previous study of darbepoetin alfa in adult patients indicated that the disposition of darbepoetin alfa administered IV or SC is similar in adult and pediatric patients, although absorption may be slightly more rapid in pediatric patients after SC dosing. The mean terminal half-life of darbepoetin alfa in this study was approximately two- to fourfold longer than that previously reported for epoetin in pediatric patients.