SummaryA total of 662 patients with mild to moderate essential hypertension were enrolled in four types of studies: (a) timolol maleate. thrce-times-a-day, (b) timolol maleate twice-a-day, (c) a combination of timolol maleate/hydrochlorothiazide and (d) a combination of timolol maleate/hydro-chlorothiazide/amiloride. The results of these studies indicated that timolol maleate used 3 or 2 times a day has a significantly greater antihypertensive activity than placebo, and that the combination of therapy with either timolol maleate/hydrochlorothiazide or timolol male-ate/hydrochlorothiazide/amiloride had a greater antihypertensive effect than each of its components.At the dose used, timolol maleate alone or in combination with hydrochlorothiazide, with or without amiloride, was a well tolerated antihypertensive agent.