Previous studies indicated calcium channel blockers to be of some help for normal-tension glaucoma patients. The present study evaluates the effect of magnesium, a 'physiological calcium blocker', in 10 glaucoma patients (6 with primary open-angle glaucoma, 4 with normal-tension glaucoma). All patients had a digital cold-induced vasospasm. Magnesium (121.5 mg) was administered twice a day for a month. After 4 weeks of treatment, the visual fields tended to improve. All three video-nailfold-capillaroscopic parameters [blood cell velocity (in mm/s) before and after cooling, cold-induced blood flow cessation (in seconds) as well as the number of capillaries per microscopic field which showed such a blood flow cessation] as well as digital temperature improved significantly. Systemic blood pressure and pulse rate remained stable. In conclusion, magnesium improves the peripheral circulation and seems to have a beneficial effect on the visual field in glaucoma patients with vasospasm.