Vascular endothelial growth factor (VEGF) is an endothelial cell growth factor expressed in normal lung tissue. The aim of the study was to investigate the expression of VEGF and its repercussions as regards alveolarization in the developing rat lung. We studied pulmonary VEGF expression at 0 and 14 days of life in Wistar rats. Rat pups were exposed to hypoxia for two hours during the first hours of life and recovered under conditions of hyperoxia or normoxia for a further two hours, or not recovered. The animals of the control group were only exposed to conditions of normoxia. Our results showed that VEGF was increased in the lungs of the animals that were exposed to hypoxia but we did not find any correlation with the septation. The VEGF was decreased in the lungs of animals exposed to hyperoxia after neonatal hypoxia. We observed this at 0 and 14 days of life, and it was correlated with a lower degree of alveolarization at 14 days of life. Our data suggest that hyperoxia after neonatal hypoxia at birth may give rise to a decrease in the expression of VEGF, possibly permanently, together with a reduction in alveolar development.