While it is well established that the acute haemodynamic effects of the beta blockers used in antihypertensive therapy vary considerably, it is still uncertain if this is true during chronic treatment. We have studied seven different beta blockers (one year follow-up): atenolol and metoprolol (cardioselective, without ISA), timolol (non-cardioselective, without ISA), and penbutolol, bunitrolol, alprenolol and pindolol (non-cardioselective, with different degrees of ISA). All drugs induced statistically significant reductions in heart rate (HR), cardiac output (CO) and blood pressure (BP) at rest as well as during exercise. During 100 and 150 W exercise CO and HR were generally decreased by 20-25% on beta blockers without ISA, less on beta blockers with strong ISA. Only in very few patients did total peripheral resistance (TPR) fall more than 10% below pre-treatment level both at rest and during exercise and TPR was not significantly reduced below pre-treatment level in any series. Drugs with combined beta-blocking and vasodilating (or alpha-blocking) properties (prizidilol and labetalol) induced clear reduction in TRP. HR was reduced, but since SI increased there was less reduction in CO on labetalol than on pure beta blockers and actually a small increase in CO on prizidilol.