Regrowth of retinal ganglion cell axons was examined 2 to 60 days after intraorbital optic nerve crush lesions in adult hamsters. Anterograde axonal transport of intraocularly injected wheat germ agglutinin-horseradish peroxidase conjugate was used to label the axons after specific postinjury time periods. Labeled axons were present in the region of the optic nerve lying between the eye and the crush site at all times, but their numbers appeared to decrease with increasing survival time. Labeled axons were first detected in the segment of optic nerve lying distal to the crush site 1 week after injury and had extended as far as 2.3 mm beyond the crush site by 60 days postinjury, growing at a rate similar to that at which the collateral branches of developing ganglion cell axons extend into their targets. Although most axons failed to regrow after these lesions, the slow reextention exhibited by members of a small population of axons indicates that the degenerating adult mammalian optic nerve provides an adequate environment for a particular mode of regrowth by injured axons of the central nervous system.