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ABSTRACT: To determine if betaxolol or timolol is present in measurable concentration in the Tenon capsule in patients under long-term topical therapy. Small (1-cc) specimens of Tenon capsule were removed at the time of filtering surgery from 15 glaucoma patients under long-term preoperative topical therapy, nine of whom had been treated with timolol and six of whom had been receiving betaxolol. Methanol extracts of these tissue samples were analyzed quantitatively for the presence of either beta-adrenergic antagonist by high-performance liquid chromatography. Drug was detected in every specimen. A mean total of 2.6 (range, 0.1-30.0) microg of betaxolol was detected per 1-cc specimen. Timolol and betaxolol penetrate the conjunctiva and accumulate in the Tenon capsule. In patients under long-term therapy, the periocular tissue can accumulate a greater quantity of beta-antagonist than is present in a daily dosage of applied eyedrops, manyfold higher than the maximal intraocular concentration.