The effect of atenolol, a beta adrenoceptor autogonist, on arterial pressure in patients with benign essential hypertension has been investigated. Eighteen patients were started on atenolol, 75 mg/day; the dose was increased at 2-wk intervals to a maximum of 900 mg if tolerated. When the maximum effective dose was determined, each patient was randomly allocated into a double-blind crossover study comparing atenolol and placebo treatments. The mean supine and erect arterial pressures of the 16 patients completing the run-in period were markedly reduced by atenolol therapy. The pretreatment mean (± SEM) supine and erect arterial pressures of the 16 patients completing the run-in period (187 ± 4.7/114 ± 2.6 and 182 ± 4.5/115 ± 3.0 mm Hg, respectively) were reduced (150 ± 5.3/97 ± 2.9 and 151 ± 5.9/100 ± 2.7 mm Hg) with atenolol therapy (p < 0.01). In the crossover study, the mean (± SEM) supine arterial pressure after 8 wk of atenolol therapy in 14 patients (144 ± 5.2/89 ± 1.7 mm Hg) was lower (p < 0.01) than at the end of placebo therapy (163 ± 4.4/105 ± 2.8 mm Hg). Similar reductions in pressure were recorded in the erect position and after exercise. No severe side effects were observed.