BACKGROUND/AIMS: To determine the medium-term effect of travoprost on the daytime intraocular pressure (IOP) of patients with normal tension glaucoma (NTG) METHODS: Newly diagnosed NTG patients underwent baseline, daytime, hourly IOP phasing. Patients were randomised to either treatment or no treatment (control). Treatment comprised once daily topical travoprost 0.004%. After 6 months, the participants underwent their second IOP phasing. RESULTS: Data from 88 participants were analysed-54 were randomised to treatment and 34 to the control group. The mean duration of treatment was 6 months. The average, maximum and minimum diurnal IOPs for treated patients were statistically significantly lower than for control patients at follow-up (p<0.001). When compared with baseline IOP, the travoprost treated group demonstrated a decrease of 16.1%, 13.5% and 16.7% in the average IOP, maximum IOP, and minimum IOP respectively. Of those treated, about one-third achieved a decrease in average IOP of at least 20%; only about one-tenth achieved a reduction of at least 30%. CONCLUSION: Travoprost monotherapy had a sustained hypotensive effect in NTG and achieved a reasonable or good response (>20% reduction in average IOP) in 32.9% of treated eyes. However, in the majority of eyes with NTG, travoprost monotherapy appeared unable to produce the desirable 30% reduction in average IOP.