Thirteen beta-blocking agents with different pharmacological properties were administered orally to 161 outpatients with essential hypertension for 5 weeks to assess their hemodynamic effects. Cardioselective ones, such as atenolol, metoprolol and acebutolol, reduced mean blood pressure (MBP) and the cardiac index (CI) without any changes of the total peripheral resistance index (TPRI). In the total 44 patients treated with these drugs, a positive correlation (r=0.529, p < 0.005) was found between the decrease in MBP and that of TPRI, but the decrease in MBP did not correlate with that of CI. Effects of non-cardioselective ones were classified arbitrarily into the following 3 patterns : 1) reduction of CI of more than 0.50 L/min/m² and a slight increase of TPRI by more than 150 dyne·sec·cm^-5·m² (nadolol, propranolol, oxprenolol and penbutolol), 2)reduction TPRI by more than 150 dyne·sec·cm^-5·m² (pindolol, bunitrolol and labetalol) and 3) the intermediate hemodynamic responses between the two patterns described above (carteolol, bupranolol and bufetolol). In all these 3 groups, the decrease in MBP correlated with that of TPRI (O the first group, n=45, r=0.557, p < 0.005 ; the second, n=37, r=0.525, p < 0.005 ; the third, n=35, r=0.612, p<0.005), but did not correlate with the decrease of CI. These results suggest that the antihypertensive effects of beta-blocking agents mainly depend on the reduction of peripheral resistance, although their pharmacological properties are not uniform and their cardiodepressant effects are variable. Reduction of cardiac performance with these beta-blocking agents seemed to be a consequence of overall pharmacological actions including beta-receptor blockade, central effects and membrane stabilizing effects, and it may be antagonized by intrinsic sympathomimetic activity and the reduction in afterload for the heart. Vascular beta-receptor blocking action may play a part in decreasing the degree of reduction of the total peripheral resistance index, while their intrinsic sympathomimetic action on the vascular site may induce vasodilating effects.