To assess the impact of booster transfusions on oxygen utilization in infants with bronchopulmonary dysplasia, we noninvasively measured oxygen consumption (VO2) and the variables of systemic oxygen transport (SOT) before and 24 hours after transfusion therapy in 10 oxygen-dependent infants with bronchopulmonary dysplasia. The infants had been born with a mean gestational age of 27.6 weeks and a mean birth weight of 0.88 kg. Study weight averaged 1.24 +/- 0.35 kg, and study age averaged 5.5 +/- 2.4 weeks. Requirements for fractional concentration of inspired oxygen averaged 0.41 +/- 0.15 to maintain an oxygen saturation of 0.93 +/- 0.02. The VO2 was measured by means of a commercially available analyzer through a flow-through circuit and pump connected to a hood or in line with the ventilator. Cardiac output was calculated by means of pulsed Doppler ultrasonography. Oxygen saturation was measured by means of transcutaneous pulse oximetry. The coefficient of oxygen utilization was calculated as VO2/SOT. Transfusion consisted of packed erythrocytes (10 ml/kg). Oxygen utilization fell in all subjects after transfusion (p less than 0.01), but it fell more substantially in subjects with higher coefficients of oxygen utilization (r = -0.80, p less than 0.01), suggesting a physiologic benefit in selected patients, particularly those with higher levels of oxygen utilization. There was also a significant increase in overall systemic oxygen transport (p less than 0.01) and decrease in VO2 (p less than 0.02). Hemoglobin levels alone did not correlate with overall systemic oxygen transport, VO2, or level of oxygen use before transfusion, and thus did not predict which subjects would have a physiologic benefit from transfusion as reflected by falls in oxygen utilization.