1. The effects of timolol alone and in combination with a fixed dose of hydrochlorothiazide and amiloride have been studied in a double-blind, controlled study in fifty-four patients with mild to moderate essential hypertension.
2. After a 4 weeks placebo period patients were randomly assigned to enter groups receiving timolol alone (group A), hydrochlorothiazide + amiloride (group B) or timolol + hydrochlorothiazide + amiloride (group C). Each treatment was carried out for 6 weeks.
3. The use of timolol (10 mg), hydrochlorothiazide (25 mg) and amiloride (2·5 mg) in a combination tablet given twice daily gave better control of blood pressure in patients with mild to moderate essential hypertension than did equivalent dosages of timolol alone or of hydrochlorothiazide and amiloride.
4. Clinical and laboratory side effects were minimal.