The efficacy of single daily doses of acebutolol, alone or combined with chlorexolone, was investigated in a group of 20 ambulant patients with uncomplicated hypertension of mild-to-moderate severity. severity. Patients were seen at fort-nightly intervals when doses were adjusted. Blood pressure was measured in all instances at 2 and 8 hours after medication, and after it had stabilized, at 26 hours after the last dose. The results indicate that a single dose of acebutolol alone produces significant lowering of supine and erect blood pressures for 24 hours (P less than 0,005). Combining chlorexolone with acebutolol does not improve the hypotensive effect of the beta-blocker significantly, but makes a smaller dose effective.