AIM: To evaluate 24 h intraocular pressure (IOP) and blood pressure (BP) with bimatoprost or latanoprost in patients with normal-tension glaucoma. DESIGN: Prospective, randomised, crossover, active-controlled, observer-masked study. METHODS: After a 6-week medicine-free period, we randomised patients to either latanoprost or bimatoprost for 8 weeks and then to the opposite medicine for 8 weeks. At baseline, and at the end of each treatment period, we evaluated IOP and BP at 08:00 and then every 2 h over the 24 h day. Diastolic ocular perfusion pressure (DOPP) was calculated from the above parameters. RESULTS: Forty completed patients had a 24 h untreated baseline IOP of 15.5 (2.3) mm Hg, and a DOPP of 59.2 (6.1) mm Hg. Both treatments lowered IOP at each time point (p<0.006), and over the 24 h curve (p<0.001, both medicines 13.1 mm Hg, 16% decrease). No difference existed between treatments in absolute IOP, at each time point, and over the 24 h curve (p>or=0.26). Additionally, no differences were found between treated 24 h systolic (p>or=0.29) and diastolic BP (p>or=0.12). The mean 24 h DOPP for latanoprost was increased from baseline (3%, p = 0.031) but not for bimatoprost (2%, p = 0.21). However, no difference in DOPP existed between treatments at any time point or over the 24 h curve (p>or=0.17). No difference was observed between treatments for any adverse event (p>0.05). CONCLUSIONS: In patients with normal-tension glaucoma, both bimatoprost and latanoprost reduce the 24 h intraocular pressure from untreated baseline to a similar extent. Latanoprost is associated with slightly improved ocular diastolic perfusion pressure over 24 h but similar absolute perfusion levels to that of bimatoprost.