We studied the effect of generally applied calcium antagonist on endothelin (ET-1) treated rabbit eyes. Nicardipine (20 micrograms/kg) was injected intravenously 15 minutes before intravitreal injection of 10 microliters of ET-1 at 10(-6) M. We measured the relative caliber of the retinal artery (the caliber of the retinal artery at the edge of the optic nerve head (ONH)/that of ONH), the capillary blood flow in ONH, visual evoked potential (VEP), intraocular pressure (IOP), and blood pressure (BP). In the control group (0.4 ml/kg of saline), administration of ET-1 caused contraction of the retinal artery, decrease of the capillary blood flow in ONH, prolongation of the VEP latency, and reduction of IOP. But these effects were significantly reduced in the calcium antagonist group. These results showed that generally applied calcium antagonist inhibits the disturbance of ocular circulation induced by ET-1. However, it also caused significant reduction of BP until 45 minutes after application, so we will have to work to find the optimum dose of calcium antagonist.