The role of neurotrophins as target-derived proteins that promote neuron survival following their retrograde transport from the terminals to the cell bodies of neurons has been firmly established in the developing peripheral nervous system. However, neurotrophins appear to have more diverse functions, particularly in the adult central nervous system. Brain-derived neurotrophic factor (BDNF), for example, produces a variety of neuromodulatory effects in the brain that are more consistent with local actions than with long-distance retrograde signalling. Here we show that BDNF is widely distributed in nerve terminals, even in brain areas such as the striatum that lack BDNF messenger RNA, and that inhibition of axonal transport or deafferentation depletes BDNF. The number of striatal neurons that contain the calcium-binding protein parvalbumin was decreased in BDNF+/- and BDNF-/- mice in direct proportion to the loss of BDNF protein, which is consistent with anterogradely supplied BDNF having a functional role in development or maintenance. Thus the anterograde transport of BDNF from neuron cell bodies to their terminals may be important for the trafficking of BDNF in the brain.