This paper examines whether adrenergic blockade (B1) may prevent the arrhythmogenic effect of acute arterial pressure (AP) elevation. In 7 anesthetized dogs iv propranolol (0.2 mg/kg) was given and in another 2 dogs stellate ganglion excision was performed. Before and after these B1 manoeuvres the AP was repeatedly increased by either elevating an open-air arterial pressure reservoir or administering iv metaraminol and decreased by abating the pressure reservoir. In a continuous recording of AP and ECG the systolic (S) AP and the presence (or absence) of ventricular arrhythmia (A) was noted. Before B1 A was noted in 652/1715 (38.0%) 5-sec periods at a SAP of 160.3 +/- 69.9 mm Hg which was significantly higher than in the 1063 5-sec periods without A (104.2 +/- 54.3) in all experiments. Following B1 it was impossible to cause A in 3 experiments. In the remaining experiments the A incidence was reduced (significantly in 5/9 experiments) to a total of 253/983 (25.7%) periods (P less than 0.001). In the 5/9 experiments with post-B1 A, the mean SAP was higher with (185.0 +/- 97.9 mm Hg) than without A (113.7 +/- 59.9 mm Hg) (significantly in 2/9 experiments). Following fitting of the SAP distributions before and after B1 to their common distribution (i.e. the same AP), the incidence of A was higher before than after B1 in all experiments (significantly in 7/9). It is concluded that B1 has an antiarrhythmic action on AP-related A. This antiarrhythmic effect seems to be due partly to an antihypertensive effect of B1 and partly to an antiarrhythmic effect of B1 for a given AP.