We used the tritiated iodoantipyrine method to estimate blood flow in the retina, optic nerve head, and retrobulbar optic nerve in monkey eyes. Twelve eyes with short-term intraocular pressure (IOP) elevation and nine eyes with long-term (up to 20 months) IOP elevation were compared with their fellow normal eyes. The eyes with long-term glaucoma were staged for degree of optic nerve damage according to disc cup size, nerve fiber layer atrophy, and histologic estimates of the remaining number of nerve fibers. At normal IOP levels, there were only minor differences in blood flow in the superior, inferior, and middle nerve head sections. In eyes with short-term IOP elevation, nerve head blood flow was normal, unless IOP exceeded 75 mm Hg. Above this level, a progressive decrease in nerve head blood flow was measured. Mean blood flow in the nerve head of eyes with long-term glaucoma was not significantly different from that in the normal fellow eyes. Some animals had small increases in blood flow, while others had small decreases. These differences from normal did not correlate with the amount or location of optic nerve damage. Our data do not support decreased blood flow as part of the pathogenesis of long-term experimental glaucoma.