The ocular morphological findings of three methyl alcohol-intoxicated rhesus monkeys with optic disc swelling was investigated with light and electron microscopy in conjunction with intravascular horse radish peroxidase. Alterations observed in the optic nerve head were confined to the axons and consisted of swelling and clustering of the mitochondria, disruption of the neurotubules, the formation of vesicles, and enlargement of the axon segments in the prelaminar region. Swelling of the oligodendroglial cytoplasm in contact with the axons and of the astrocytes was seen in the retrolaminar optic nerve and the intraorbital optic nerve. Alterations were not observed in the retina. It is hypothesized that the alterations in the axons are the result of disrupted axoplasmic flow. Possible mechanisms relating methyl alcohol intoxication to disruption of axoplasmic flow are discussed.