Insulin-like growth factor-I (IGF-I) is a pleiotropic protein that acts on many tissues and organs. As it is one of the major trophic factors in the circulation, its actions in peripheral tissues are well established. It has been used for the treatment of several diseases, including growth deficiency, osteoporosis, catabolic disorders and diabetes. Recent evidence supports the significance of IGF-I in the maintenance of the integrity and homeostasis of the nervous system. The widespread distribution of its receptor allows IGF-I to affect the survival of numerous populations of neurones and glial cells in both the CNS and the PNS. Most recently, a clinical trial has revealed the beneficial effects of IGF-I in amyotrophic lateral-sclerosis (ALS), a degenerative disease of the motoneurones. We review briefly here experimental and clinical information that suggests the potential usefulness of IGF-I in the treatment of certain neurodegenerative diseases, including ALS, Alzheimer's disease, various neuropathies and brain trauma. The rather unique propensity of IGF-I to act on a variety of neuronal cells might provide a general means of reducing or slowing down neuronal losses that occur following various brain insults.