It has been demonstrated in humans that there are high vitreous concentrations of VEGF in eyes with active neovascularization (6,14). In the same way, the animal models of ROP report high levels of VEGF (2,21). The levels of this growth factor are altered in both stages, with a more marked increase during the first stage (2). Some clinical studies in patients with ROP in stage 4 and 5 have reported an increase of up to 90 times greater of the concentration of VEGF in the subretinal liquid in comparison with the found in patients with retinal detachment of any other cause (1). Finally, when it has been possible to examine retinas immediately after the treatment (due to death of the patient) have been found a low expression of mRNA of VEGF in the treated cells (6).