The objective of this 12-week double-blind randomized multicentre study was to compare the efficacy and tolerability of nebivolol, a recently developed beta-blocking agent with vasodilating properties, to the classical beta-blocker atenolol. After a placebo run-in phase, 205 mild-to-moderate middle-age essential hypertensives were randomized to either nebivolol 5 mg daily (n = 105) or atenolol 100 mg daily (n = 100) over a period of 12 weeks. The primary endpoint of the study was the change in sitting systolic and diastolic blood pressure (SBP and DBP respectively) from baseline to week 12 of treatment. The two drugs induced similar significant antihypertensive effects, the SBP and DBP reduction amounting to -18.2 +/-14.0 and -14.6 +/-7.9 mmHg (mean +/- SD) for atenolol and -19.1 +/-12.9 and -14.8 +/- 7.1 for nebivolol (p < 0.01 for all). This was the case also for standing blood pressure. Sitting and standing heart rate values were significantly reduced by both drugs, the bradicardic response induced by nebivolol treatment being significantly less than atenolol. Distribution of responders and non- responders was similar for nebivolol and atenolol, while the former drug showed a better tolerability profile and a lower incidence of side-effects. These data provide evidence, that, for the same antihypertensive effects, nebivolol shows a better tolerability profile than atenolol and a lower incidence of adverse effects.