The importance of testosterone in desire, interest and sexual motivation is well known, but its effects on erectile function continue provoking controversy. Data obtained in animals under experimental or surgical castration, explains how this condition can cause a veno-occlusive dysfunction and therefore an erectile dysfunction. In a model of animal flebogenous erectile dysfunction, the intracavernous vascular endothelial growth factor (VEGF), together with testosterone, reestablishes the balance between the muscle and the conjunctive tissue, hypertrophy and hyperplasia of endothelial cells and regularizes the diameter of dorsal nervous cells, thus preventing the veno-occlusive dysfunction. Castration also induces the apopthosis in the erectile tissue of the penis; the treatment with testosterone provokes a new DNA synthesis.