Atenolol, Pindolol and Propranolol in single daily doses administered to 18 selected patients with mild essential hypertension achieved adequate control of blood pressure. Chlorothiazide had been initially administered twice a day without full control of blood pressure and this diuretic therapy was continued unaltered throughout the study. Methacholine challenge testing of respiratory function was performed during the placebo phase and with each beta adrenoreceptor-blocking drug. In the 18 non-asthmatic patients, the reduction in FEV1, was significant only for propranolol therapy when compared to placebo. Each beta adrenoreceptor-blocking drug was associated with small, but significant, increases in fasting plasma triglyceride concentrations and suppression of fasting immuno-reactive glucagon concentrations.