Two premature infants who had episodes of hemolysis following blood transfusion are described. No incompatibility was found between donor and infant in either case. Further investigation of the donors' blood excluded other possible causes of hemolysis. The only anomaly found was that the donors were glucose-6-phosphate dehydrogenase (G6PD) deficient, while the infants had normal G6PD activity. Our report describes a new possible cause of hemolysis in preterm infants, and suggests that screening for G6PD deficiency may be necessary before blood is transfused to a preterm infant.