We compared the effects of oral nadolol 20 mg once daily and topical timolol 0.25% twice daily on the intraocular pressures of 22 glaucoma suspects, in a 12 week double-masked crossover study. Both nadolol and timolol reduced intraocular pressure (p less than 0.001). The reductions in intraocular pressure did not differ significantly after two weeks and four weeks of treatment. Nine of these subjects underwent treadmill exercise tests in order to compare the effects of nadolol and timolol on the cardiovascular system. The effects of the two treatments on blood pressure were comparable, but nadolol caused a significantly greater reduction in heart rate than timolol at rest (p less than 0.05). Nadolol reduces intraocular pressure effectively and may prove a useful alternative treatment for chronic simple glaucoma.