The view that gonadal steroids are only reproductive hormones has completely changed over the past years. A large number of experimental studies, most performed in rodents, have indeed demonstrated the multiple actions of steroids throughout the nervous system. Thus, progesterone, a steroid hormone well known for its role in the maintenance of pregnancy, has been shown to promote the viability and regeneration of neurons and also to play a role in the formation of myelin sheaths, which protect the axons and are required for the efficient conduction of electrical impulses along nerve fibers. Pregnenolone, progesterone and its reduced metabolites are qualified as "neurosteroids", because they can be synthesized by neurons and glial cells within the nervous system. In response to traumatic brain injury or spinal cord lesion, the local formation of pregnenolone and progesterone is increased, strongly suggesting that this response may be part of the mechanisms by which nerve cells cope with neurodegeneration. However, the increase in endogenous neurosteroids in response to a lesion is not sufficient for optimal neuroprotection or myelin repair, as the administration of exogenous progesterone has marked protective and trophic effects on neurons and oligodendrocytes. There is thus a potential for therapeutic interventions to promote neuroprotection and neuroregeneration, either by stimulating the synthesis of endogenous neurosteroids or by administering exogenous progestagens.