Anemia of prematurity (AOP) has been conventionally treated with erythrocyte transfusions. Recent investigations have reported the use of recombinant human erythropoietin (rHuEPO) as an alternative for treating AOP. The potential of rHuEPO in increasing erythropoiesis implies its clinical usefulness. The effect of rHuEPO on reticulocyte count as well as other parameters of blood cells was examined in 14 premature babies with AOP. The average birth body weight and gestational age of these premature babies were 1533.71 +/- 61.66 g (Mean +/- SEM) and 31.36 +/- 0.49 weeks respectively. They received the first dose of rHuEPO at age 26.14 +/- 2.03 days with a hemoglobin level by 9.40 +/- 0.27 g/dL and hematocrit level of 28.20 +/- 0.81%. They were given rHuEPO 200 U/kg subcutaneously every other day for 10 doses, and iron 3 mg/kg and vitamin E 25 IU/kg per os every day. Average erythropoietin level of the patients on entry into this study was low (7.66 +/- 1.10 mu/mL). After treatment with rHuEPO for 20 days, the corrected reticulocyte count increased from 0.64 +/- 0.10% to 1.68 +/- 0.42% on Day 5 (P < 0.05), 1.96 +/- 0.41% on Day 12 (P < 0.05), 1.77 +/- 0.43% on Day 20 (P < 0.05), and hematocrit increased from 28.2 +/- 0.81% to 29.58 +/- 1.02% (p < 0.05) on Day 20. Bone marrow aspirates on Day 10 for 9 infants revealed moderate to high cellularity, mostly with erythroblasts (47.89 +/- 1.78%); the M/E ratio was low (0.57 +/- 0.05). The granulocyte series and megakaryocyte could be well visualised.(ABSTRACT TRUNCATED AT 250 WORDS)