OBJECTIVE To investigate the 24 h effects of bimatoprost 0.01% monotherapy on intraocular pressure (IOP) and ocular perfusion pressure (OPP). METHODS Prospective, open-label experimental study. METHODS Single tertiary ophthalmic clinic. METHODS Sixteen patients with diagnosed primary open-angle glaucoma (POAG) or ocular hypertension (ages, 49-77 years). METHODS Baseline data of 24 h IOP in untreated patients were collected in a sleep laboratory. Measurements of IOP were taken using a pneumatonometer every 2 h in the sitting and supine body positions during the 16 h diurnal/wake period and in the supine position during the 8 h nocturnal/sleep period. After baseline measurements were taken, patients were treated with bimatoprost 0.01% one time per day at bedtime for 4 weeks, and then 24 h IOP data were collected under the same laboratory conditions. METHODS Diurnal and nocturnal IOP and OPP means under bimatoprost 0.01% treatment were compared with baseline. RESULTS The diurnal and nocturnal IOP means were significantly lower under the bimatoprost 0.01% treatment than baseline in both the sitting and supine positions. The diurnal and nocturnal OPP means were significantly higher under treatment than baseline in both the sitting and supine positions. CONCLUSIONS Bimatoprost 0.01% monotherapy significantly lowered IOP and increased OPP during the 24 h period.