A double-masked cross-over comparison of the ocular hypotensive effect in 19 glaucoma patients between timolol 0.5% - a non-selective beta-blocking agent - and metoprolol 3% - a beta 1-selective blocking agent - disclosed a greater pressure lowering effect (mean 9%, median 7% more) with timolol in a treatment period of 1 month. In patients on timolol treatment 47% - 60% of the eyes could be controlled on an IOP level less than 20 mmHg compared to 34% - 47% of the eyes treated with metoprolol. Metoprolol induced a transitory burning sensation in the eyes of 58% patients compared to 26% treated with timolol. Possible signs of dry eyes manifestations as measured by break-up time, rose bengal and fluorescein 1% staining, tear osmolality and Schirmer test I developed in both the timolol (4 patients) and metoprolol (3 patients) treated group. No significant influence on blood pressure and heart rate was observed. In none had the visual field or visual acuity deteriorated at the end of the study.