The effect of blood transfusion on the occurrence of RLF was evaluated in 58 infants who weighed less than 1001 g at birth (Group I) and 70 oxygen treated infants of various birth weights (Group II). Although there was no significant difference between Group I infants with or without exchange transfusion as to birth weight, gestational age, duration of oxygen therapy, peak Pa02's, or multiple births, there was a significantly increased incidence of pre-retrolental fibroplasia in transfused over non-transfused Group II infants. When Group II infants were stratified for prematurity and oxygen duration, this difference persisted in those not already at risk for RLF. This increased incidence of retinopathy in transfused infants suggests that blood transfusion may be a risk factor in the pathogenesis of RLF.