In an eight-week study, timolol maleate ophthalmic solution 0.25% was administered twice daily with either pilocarpine 2% four times a day, epinephrine 2% twice a day, carbachol 1.5% four times a day, or 250 mg of acetazolamide twice a day to 44 patients with chronic open-angle glaucoma. Compared to baseline readings on standard therapy alone, mean intraocular pressure was significantly reduced after addition of timolol maleate to each of the regimens. Mean facility of outflow was unaffected. No clinically significant ocular irritation or changes in visual acuity, pupil size, or vital signs were observed in any patient. Timolol maleate appears to be effective and well tolerated when administered with other antiglaucoma medications in patients with open-angle glaucoma.