Purpose The objective of the study was to compare the intraocular pressure (IOP)-lowering efficacy and safety of travoprost 0.004%/timolol 0.5% ophthalmic solution (Trav/Tim) to latanoprost 0.005%/timolol 0.5% ophthalmic solution (Lat/Tim), dosed once daily in the morning, in patients with open-angle glaucoma (OAG) or ocular hypertension (OH). Methods This was a randomized, double-masked, multicenter, parallel group, active-controlled study conducted at 41 sites. At the eligibility visit the patients were randomized (1:1) to the assigned masked medication if they met inclusion/exclusion criteria, and the mean IOP values in the eligible eyes were ≥24 mmHg at 9 AM and ≥21 mmHg at 11 AM and 4 PM. Patients were excluded if the mean IOP in either eye was >36 mmHg. Patients were instructed to administer the assigned medication each morning at 9 AM. During the treatment phase of the study, IOP was measured at 9 AM at week 2, week 6, month 3, and month 9. At the month 6 and month 12 visits, IOP was measured at 9 AM, 11 AM, and 4 PM. Statistical methods included a repeated measures analysis of variance (ANOVA); to test for noninferiority, a 95% confidence interval for the treatment group difference was constructed based on the ANOVA results for each time point at month 12. Results Patients (n=408) with OAG or OH were enrolled at 41 sites. One patient withdrew prior to receiving medication so 207 in the Trav/Tim group and 200 in the Lat/Tim group were evaluable for safety. Baseline demographic characteristics as well as IOP values showed no statistical differences between the two groups. Trav/Tim provided lower mean IOP values than Lat/Tim that were statistically significant at the week 2 9 AM (p=0.0081), month 6 9 AM (p=0.0056), and month 6 11 AM (p=0.0128) time points and at 9 AM time point pooled across all visits (p=0.0235) when mean IOP was 0.6 mmHg lower in the Trav/Tim group. Treatment-related adverse events were mild in both groups. Although hyperemia was reported from a higher percentage of patients in Trav/Tim group, differences in average hyperemia scores between the two groups were not considered clinically relevant. Conclusions Travoprost 0.004%/timolol 0.5% ophthalmic solution produced mean IOP levels that are statistically noninferior to latanoprost 0.005%/timolol 0.5% ophthalmic solution. Furthermore, at 9:00 AM, 24 hours after dosing, IOP was statistically lower for travoprost 0.004%/timolol 0.5% pooled across all visits. Travoprost 0.004%/timolol 0.5% fixed combination ophthalmic solution is an effective treatment for reducing IOP and it is safe and well-tolerated in patients with OAG or OH. (Eur J Ophthalmol 2007; 17: 183–90)