In the rat, intracerebral injection of bacterial hyaluronidase resulted in the almost complete disappearance of hyaluronic acid (HA) and glial hyaluronate-binding protein (GHAP) from cerebral hemispheres, brain stem, and cerebellum (but not from optic nerves and chiasm) starting 2-3 hr after the injection. HA and GHAP reappeared throughout the brain in characteristic patches 2-3 days after the injection. The patches gradually became confluent and after 12 days the brain appeared virtually normal. In normal rat optic nerve, staining for HA and GHAP ceased abruptly in the region of the lamina cribrosa. The retina was completely negative. HA and GHAP disappeared from hyaluronidase-injected optic nerve, chiasm, and contralateral optic nerve. In hyaluronidase-injected crushed optic nerves, regenerated axons were able to grow for short distances (about 500 microns) into the distal stump undergoing Wallerian degeneration. No such growth was observed in saline-injected controls.