Improvement in the efficacy of newer antihypertensive agents has resulted in consideration of the side effects of drug therapy. Impairment of memory function resulting from antihypertensive therapy has been clinically suspected. This observation has been supported by a study in which the effects of methyldopa and propranolol on memory function were reported. Recently, memory function has been assessed in a group of patients treated with either a beta-blocker (atenolol) or an angiotensin-converting enzyme inhibitor (enalapril) in a randomised, observer-blind study in moderate essential hypertension. The patients were assessed, on placebo and after 16 weeks of treatment on active therapy, by use of a series of 4 memory function tests related to everyday life. In the hypertension study group, 13 received atenolol and 12 received enalapril. Similar reduction of diastolic pressure occurred in both groups, but systolic pressure was significantly reduced in the enalapril group (p less than 0.05). In the atenolol group memory performance scores were consistently lower than in the placebo phase in 9 of 28 estimates of memory function. In the enalapril group there were no significant changes. The study indicated that atenolol might produce mild memory impairment, whereas enalapril was devoid of any measurable effect on memory function.