This multicenter, randomized, double-blind clinical trial was undertaken to compare the intraocular pressure (IOP)-lowering efficacy and safety of topical bimatoprost 0.03% with that of latanoprost 0.005% for the treatment of patients with normal-tension glaucoma. After washout of all ocular hypotensive medications, patients with normal-tension glaucoma (n=60) were randomly assigned to oncedaily bimatoprost 0.03% or latanoprost 0.005% for 3 mo. Diurnal IOP measurements were taken at each study visit. Primary outcome measures consisted of mean change from baseline IOP (8 AM, Noon, 4 PM) and change in visual field. Secondary measures included mean IOP, ophthalmologic examination findings, results of clinical evaluation, and adverse events. Mean change from baseline IOP at each study visit was statistically significant at all diurnal measurements for patients taking bimatoprost and for those taking latanoprost (P<.001). The 8 AM mean change from baseline IOP measurement showed a significant between-group difference (P< or =.033) in favor of bimatoprost at both follow-up visits. After 3 mo of treatment, mean IOP reductions from baseline ranged from 2.8 to 3.8 mm Hg (17.5%-21.6%) with bimatoprost and from 2.1 to 2.6 mm Hg (12.7%-16.2%) with latanoprost. Overall mean reduction in IOP after 3 mo of treatment was 3.4 mm Hg (19.9% rpar; with bimatoprost and 2.3 mm Hg (14.6%) with latanoprost (P=.035). No significant between-group differences were observed in incidence of adverse events, clinical success, or demographic variables. Bimatoprost was found to be more effective than latanoprost in lowering IOP in the patient with normal-tension glaucoma. Both drugs were efficacious and well tolerated.