Ocular blood flow was studied in newborn piglets during light exposure and light combined with hyperoxia. Light caused a significant increase in ocular blood flow which returned to values not significantly different from baseline levels during superimposed hyperoxia. None of these experimental conditions changed total cerebral blood flow or cardiac output. The findings indicate that light might be a regulator of ocular blood flow. This influence of light on ocular blood flow may be of importance in the pathophysiology of retinopathy of prematurity.