In an open-label 12-week study, the safety and efficacy of bimatoprost 0.03% was evaluated in 55 patients with open-angle glaucoma or ocular hypertension inadequately controlled by topical beta-blocker monotherapy. Patients discontinued their topical beta-blocker therapy at the baseline visit and began bimatoprost monotherapy that evening. Study visits were at 6 and 12 weeks postbaseline. Bimatoprost reduced intraocular pressure (IOP) 4.5 mm Hg (21.5%; P < .001) from baseline at week 6 and 4.2 mm Hg (19.6%; P < .001) at week 12. Patients were more likely to achieve low target pressures with bimatoprost than with topical beta-blockers. Conjunctival hyperemia was the most commonly reported adverse event. The findings from this study indicate bimatoprost monotherapy provides a substantially greater IOP reduction than topical beta-blocker therapy and allows more patients to achieve a low target pressure. Bimatoprost is an effective alternative to topical beta-blockers for the treatment of glaucoma and ocular hypertension.