The pharmacokinetics of recombinant human erythropoietin was studied in 12 very low birth weight preterm infants < 32 weeks of gestation after subcutaneous administration of 300 IU/kg at a postconceptional age of 34 (32-37) weeks and a weight of 1,505 (1330-1,740)g (median and range). The administration of recombinant human erythropoietin produced a rapid increase in serum erythropoietin levels with a peak level of 362.8 mIU/ml at 8.9 h. The area under the curve was 8,177.5 (4,597.1-15,453.0) mIU/ml/h, the absorption half-life was 5.5 (1.6-6.6) h, the elimination half-life was 7.9 (5.6-19.4) h, and the residence time was 19.6 (5.1-32.6) h (all values reflect median and range). There was no significant correlation between absorption and elimination half-life of erythropoietin and birth weight, gestational age, sex, and age and weight of the infants at the time of administration of erythropoietin. Based on absorption and elimination kinetics, the dosing interval for subcutaneous administration must not be < 48 h.