We compared the capillary blood-cell velocity in the fingertips of 30 patients with high-tension glaucoma, 30 patients with normal-tension glaucoma, and 30 control subjects by nailfold capillaroscopy. There were no measurable differences in the morphologic findings. The blood-flow velocity, however, was reduced significantly in the patients with normal-tension glaucoma compared with the control subjects (P less than .05). This difference was especially pronounced after cold provocation (P less than .0005). After cooling, 25 of 30 patients with normal-tension glaucoma had a blood standstill of 12 seconds or more, whereas only three of 30 control subjects and four of 30 patients with high-tension glaucoma had a measurable blood standstill.