We produced retrobulbar hematoma in both orbits of 10 pigs in order to assess the effects of blood elements and pressure created by the hematoma on the optic nerves. Ten other pigs were used as a control group. Following decompression in the right orbits, ocular movements, fundi, and intraocular pressure were evaluated for 6 weeks. At the end of the 6th week the optic nerves of 20 pigs were dissected bilaterally for measurements of ATP-ase activity and ultrastructural examination. The results of the ultrastructural examination of the optic nerves of the control group were normal. Optic nerves with decompressed retrobulbar hematoma showed minimal degeneration, whereas the nerves subjected to retrobulbar hematoma with no decompression showed significant degenerative changes. For all groups ATP-ase activities were measured and evaluated. Na+, K+ ATP-ase activities decreased, while Ca++, Mg++ ATP-ase activities increased with the extent of degeneration. Optic nerve damage can develop after trauma. Decompression procedures are not among the causes of optic nerve degeneration but retrobulbar hematoma can result in optic neuropathy caused by the compression from the hematoma and the direct effect of blood waste products on the optic nerve.