Acute proliferative retrolental fibroplasia (RLF) has been studied in premature infants employing a Zeiss fundus camera and fluorescein angiography. A total of 164 angiograms have been performed on 122 infants. At the present time, angiography is reserved for studying infants with peculiar or puzzling fundus pictures. A dose of 0.1-0.4 cc of 10% sodium fluoresceinate is employed, depending on the age and the weight of the baby. Fluorescein clearly outlines the major arteriovenous shunt in the retina, which is the hallmark of acute RLF. The shunt fills with fluorescein and leaks it profusely. On regression, a fine brush border of capillaries is seen in the region where the shunt previously had been located. Study of the population susceptible to RLF reveals it to be the smallest sickest babies in the premature nursery.