Axonal outgrowth following a crush of the goldfish optic nerve was enhanced if nerve growth factor (NGF) was administered by intraocular injection or by local application to the lesion site. Various forms of NGF (beta, 2.5S and 7S) were effective, producing a 20-40% decrease in the time required for recovery of the startle reaction to a bright light. A corresponding increase in axonal outgrowth was revealed by histological examination of the optic nerves. The effect produced by a single intraocular injection given at the time of the lesion was not further increased by subsequent injections. Up to 14 days after the lesion, the size of the retinal ganglion cell bodies and the incidence of nucleoli detectable by light microscopy were not affected by the NGF treatment.