This prospective study compared intraocular pressure (IOP) control, cardiorespiratory function, and adverse effects in 50 patients with glaucoma and ocular hypertension. Patients on topical combination timolol-latanoprost therapy were recruited. After they had used this combination for at least 2 months, they were switched to bimatoprost monotherapy. Full ocular examination and spirometric testing were performed; a questionnaire concerned with ocular symptoms was completed, and pulse rate was recorded. Two months later, mean IOP was similar with the combination (17.2 mm Hg) and with bimatoprost (16.4 mm Hg), but mean peak expiratory flow rate, ratio of forced expiratory volume in 1 second to forced vital capacity, and heart rate had increased significantly after the switch was made to bimatoprost. Adverse effects generally were similar with these regimens; however, the incidence of hyperemia doubled after the switch had been made. Bimatoprost and the timolol-latanoprost combination were equally efficacious in lowering IOP; bimatoprost had less of an effect on cardiorespiratory function.