Neuronal death in vertebrate development is widely believed to be regulated by retrograde survival signals from the axonal target territory, and these signals are assumed to be initiated by the binding of trophic molecules to the axon terminal. However, direct evidence for the retrograde transmission of such survival signals along developing axons is only available in the peripheral nervous system. We show here in a central projection, the isthmo-optic projection of chick embryos, that a neurotrophin, brain-derived neurotrophic factor, can indeed initiate retrograde survival signals from the target territory. A related molecule, neurotrophin-3, is ineffective.