We evaluated the safety and effectiveness of adding topically administered betaxolol 0.5% twice daily in 39 patients with ocular hypertension or primary open-angle glaucoma already being treated with dipivefrin 0.1% twice daily. The addition of the betaxolol significantly decreased (P less than .01) the mean intraocular pressure after two weeks (2.82 mm Hg) and four weeks (3.63 mm Hg). There were no significant changes in pulse rate, mean arterial pressure, or pupil diameter. The administration of betaxolol to patients already receiving dipivefrin appears to be clinically useful.