The origin and movement of neurotrophic factors such as brain-derived neurotrophic factor (BDNF) between nerve cells has been controversial. Kohara et al. used BDNF tagged with green fluorescent protein to follow anterograde synaptic transport from axons of neurons to postsynaptic cells. This synaptic transport of the growth factor is absent when neuronal activity was blocked by tetrodotoxin and was enhanced after reduction of inhibition. These results constitute direct evidence for an anterograde, trans-synaptic transport of BDNF.