Timolol maleate, a potent beta-adrenergic antagonist, reduces intraocular pressure in rabbits. With topical application in one eye, a significant reduction in pressure is seen in the contralateral, untreated eye also. When used in conjunction with timolol, other adrenergic amines, such as norepinephrine and epinephrine, produce an additional hypotensive response. On the other hand, pretreatment with timolol does inhibit the ocular hypotensive response to topically applied albuterol. No further reduction in pressure is seen after application of this beta-adrenergic agonist to eyes pretreated with timolol. In a double-blind study with patients who had previously been receiving various medications for control of elevated intraocular pressures, timolol was as effective as pilocarpine in reducing intraocular tension. Many common complaints associated with pilocarpine therapy, including miosis, ocular irritation, and blurred vision, were not encountered with timolol therapy.