We determined the effects of either topical or systemic calcium channel antagonists on rabbit intraocular pressure (IOP). Topical nifedipine, verapamil or diltiazem had no significant effect on IOP. Intravenous verapamil and nifedipine caused statistically significant reductions in IOP between 2 and 6 h after administration; the nifedipine response followed an increase in IOP at 30 min. Diltiazem, given 3 times daily for 3 days, caused no pressure change. In the rabbit, therefore, calcium channel antagonists have no effect when given topically, but do reduce IOP when given systemically.