This study is aimed at establishing the efficacy of the therapeutic agent, betaxolol, in diurnal control of IOP (intraocular pressure). Therapy was performed on 32 eyes affected by POAG (primary open-angle glaucoma) and 16 eyes affected by NTG (normal-tension glaucoma). Two preparations of betaxolol were utilized: betaxolol hydrochloride 0.50% (Betoptic) was administered to 15 POAG and 7 NTG eyes; betaxolol hydrochloride 0.25% ophthalmic suspension (Betoptic S) was administered to 17 POAG and 9 NTG eyes. IOP measurements were taken every two hours from 8 a.m. to 8 p.m. IOP was measured before therapy and at 12 hours, 30 days, and 3 months of therapy. Betaxolol hydrochloride 0.50% was more effective at lowering IOP during the day. Diurnal pressure peaks, which are a risk factor concerning the maintenance of visual field in glaucoma patients, were also reduced using 0.50% betaxolol hydrochloride.