The efficacy of atenolol given once daily was assessed in 41 otherwise healthy hypertensive patients over a period of six months. Twelve patients whose blood pressure was not well-controlled on methyldopa and chlorthalidone and 11 patients who were treated previously with other beta-blockers all benefited from atenolol which appeared to be effective and well-tolerated. Ten patients complained of fatigue not necessarily related to a drop in blood pressure, and two of head-ache. Respiratory functions were assessed in a double blind trial on 30 patients. No significant changes in any of the expiratory flow rates were recorded after three months of continuous treatment with atenolol in either smokers or nonsmokers.