The effect of low-energy laser irradiation, known to delay axonal degeneration in mechanically traumatized nerves, was investigated in rabbit retinal ganglion cells damaged by temporary anoxia. Complete retinal vascular occlusion was induced in 39 rabbits by application of pressure to the cornea, with continuous monitoring under an operating microscope. The duration of occlusion was 15, 30 or 60 minutes. Starting immediately after the cessation of vascular occlusion, half of the rabbits in each group received transcorneal irradiation with a 35-mW helium-neon laser for 5 minutes daily on 10 consecutive days. The nonirradiated rabbits served as controls. Retinal ganglion cell viability was demonstrated by retrograde labeling of their axons with horseradish peroxidase, introduced subdurally into the optic nerve at a distance of 2 mm distal to the globe, 48 hours prior to sacrifice. For labeling intensity controls we used normal, not occluded, animals labeled with horseradish peroxidase by the same method. The animals were sacrificed 2, 4 or 8 weeks after occlusion. Labeling of retinal ganglion cells and their axons was observed in 100% of the normal control animals and in 85% of the irradiated rabbits. The results suggest that low-energy helium-neon laser irradiation attenuates the damage inflicted on the retinal ganglion cells as a result of anoxia.