Anaemia of prematurity, a postnatal fall in haemoglobin concentration and haematocrit, is particularly common in those born at less than 32 weeks of gestation. Experimental and clinical data implicate inadequate erythropoietin production as an important reason. In this study recombinant human erythropoietin (r-HuEpo) was used in an attempt to treat or prevent this anaemia and thereby provide an alternative to erythrocyte transfusions. Premature infants (birth weight < or = 1250 g and gestational age < or = 32 weeks), who were likely to need transfusions, were randomly assigned to receive 4 weeks of treatment with either subcutaneously administered r-HuEpo (200 U; n = 12) or placebo (n = 12), three times weekly. All patients had oral supplements of elemental iron at a dose of 3 mg/kg/day. Treatment was started in the third week of life. Reticulocyte counts were significantly raised (P < 0.05) in the group treated with r-HuEpo at the end of treatment. The neonates in the group treated with r-HuEpo needed fewer erythrocyte transfusions than those in the placebo group during treatment. There were no toxic effects attributable to r-HuEpo. The results indicate that treatment of infants with very low birth weights with r-HuEpo will reduce their need for erythrocyte transfusions.