We have compared the efficacy and pharmacokinetics of bisoprolol, a new cardioselective beta-adrenoceptor antagonist, with atenolol in a randomized double-blind crossover study in 12 patients (mean age 53.5 y) with mild to moderate essential hypertension. After a two week placebo wash-out period without any antihypertensive therapy, the patients were given bisoprolol 10 mg daily or atenolol 50 mg daily, increasing to 20 mg or 100 mg respectively if the sitting diastolic blood pressure did not fall below 90 mm Hg after two weeks of therapy. Crossover occurred after six weeks of active therapy followed by two weeks of placebo wash-out. After 6 weeks of therapy both drugs significantly reduced sitting and standing diastolic blood pressures (bisoprolol by 15% and 16% respectively, atenolol by 11% in both cases). However, while sitting and standing systolic pressures were significantly reduced by bisoprolol (13% and 16% respectively), only standing systolic pressures were significantly reduced by atenolol (11%), and this reduction was significantly less than with bisoprolol (p less than 0.05). Both drugs similarly reduced mean sitting and standing heart rates. There were no significant differences between the single-dose and steady-state kinetics of either bisoprolol or atenolol. The mean plasma elimination half-life (t1/2) increased from 12.9 to 13.2 h during steady state on bisoprolol and from 7.2 to 11.5 h on atenolol. The apparent volume of distribution (Vz) was greater for bisoprolol than for atenolol after single dosing (235 1 vs 146 1) and at steady state (216 1 vs 137 1), but clearances were similar for both drugs.(ABSTRACT TRUNCATED AT 250 WORDS)