Metipranolol is a non-cardioselective beta adrenergic blocking drug used in the treatment of glaucoma. 56 patients with intraocular pressure between 30-49 mm hg were randomised to one of six treatment regimens for a 12 week period. Each patient received each concentration for 4 weeks and intraocular pressures were checked every two weeks. Using a worst and an average eye approach, mean initial intra-ocular pressures were 35.8 and 35.0 mm hg respectively. The mean fall in intra-ocular pressure after 4 weeks treatment ranged from 12.8 (0.1%) to 14.1 mm hg (0.6%) for average eyes (n = 56), and from 13.4 to 16.7 mm hg for worst eyes. These differences were not statistically significant (p greater than 0.05-p greater than 0.5). Increasing the concentration had no significant effect on pressure. Reducing the concentration had no effect except in patients who changed from 0.6% to 0.1%, when there was a mean rise of approximately 2 mm hg, p less than 0.02. The incidence of stinging varied from 19% of attendances on 0.1%, to 63% on 0.6%. We recommend the use of the 0.1% strength since all three significantly lower intra-ocular pressure but the higher concentrations are more expensive, cause more stinging, and are no better at lowering intra-ocular pressure.