Optic nerve axonal transport was previously shown to be blocked at the level of the lamina cribrosa by elevated intraocular pressure. To discover if this blockage might be secondary to pressure-induced ischemia, the effect of unilateral common carotid artery ligation upon the pressure-induced interruption of axonal transport was studied. In 13 owl monkeys (A. trivirgatus), the right common carotid artery was ligated within the anterior cervical triangle. Ophthalmodynomometry was performed on all experimental eyes 3 days later. In 9 of the 13 animals, this estimate of ophthalmic artery pressure was 10-20 mm Hg less in the right compared to the left eye. Optic nerve axonal transport was studied in right and left eyes during 5 h of increased intraocular pressure (ocular pressure 35 mm Hg less than mean femoral artery blood pressure). No significant difference in the extent to which the transport mechanisms were interrupted could be demonstrated when comparing right and left eyes of the experimental animals. No vascular mechanism for this pressure-induced interruption of axonal transport was supported.