The effect of long-term treatment of hypertension with propranolol, alone or in combination with hydrochlorothiazide and/or dihydralazine, was investigated in 93 patients with various types of hypertension. Normalisation of the B. P. was obtained within two-four weeks of treatment with propranolol alone in all cases with mild hypertension, and in 77% and 44% of moderate and severe forms respectively. These percentages were even higher when propranolol was employed with hydrochlorothiazide and/or dihydralazine. The rationale of this combination and the mechanism of the hypotensive effect of propranolol are discussed. The drug was well tolerated; major side effects did not occur.