SummaryHaemodynamic studies were performed in 11 hypertensive patients, first while they were receiving placebo and then after one months treatment with a beta-adrenergic blocking agent (I.C.I. 66,082).An average fall in mean arterial blood pressure of 26.2 mmHg was obtained. Although the mean total peripheral resistance showed little change, data from individual patients show a correlation between changes in blood pressure and resistance. There was no correlation between fall in pressure and fall in cardiac output.