Fifty patients with chronic open-angle glaucoma were studied in a double-blind study with Timolol ophthalmic solution, in a concentration of 0.1%, 0.2% and 0.5%, and Pilocarpine eye drops 1%, 2% and 4% over a period of seventeen weeks. Timolol was instilled twice daily into the conjunctival sack, or Pilocarpine four times daily. The results of the investigations may be summarised as follows: Timolol (0.1%-0.5%) achieved a mode-rate reduction in I.O.P. of 29%, compared to a 10.3% drop with Pilocarpine (1%-4%). Under treatment with Timolol, there was a statistically significant reduction in pulse rate of 12%, also a slight drop in blood-pressure of 3.5% systolic and 2.5% diastolic. During this study, those treated with Timolol showed no statistical changes of visual acuity, visual field, or on slit lamp examination and ophthalmoscopy of the optic disk and retina. The average pupillary diameter and tear flow (Schirmer Test), were little changed in the group of patients treated with Timolol, whereas in the Pilocarpine group, the size of the pupil decreased by 30.5% as expected.