The use of intracerebral NGF (nerve growth factor) infusions as a therapeutic tool to prevent the degeneration of cholinergic neurons in humans suffering from Alzheimer's disease has recently been suggested. In the present study, intracerebroventricular infusion of nerve growth factor into the adult rat brain was found to induce axonal sprouting of mature, uninjured axons associated with the intradural segment of the internal carotid artery. Following NGF infusion, a three-fold increase in the total number of axons associated with the vessel wall was observed when compared with vehicle-infused animals. This vascular hyperinnervation might also occur in humans. Before NGF infusion therapy is initiated, more research is necessary concerning the specificity, mechanisms, and functional significance of the sprouting response observed in this study.