To investigate whether the lower the blood pressure (BP) the better the prognosis for the patient with moderate-to-severe hypertension, an assessment was made of 902 patients who received the beta 1-selective beta-blocker atenolol (median dose 100 mg a day), either alone or with other antihypertensive agents, for up to 10 years (mean 6.1). 91 died, 40 from myocardial infarction, 21 from stroke, and 30 from other causes. Initial BP was a poor predictor of mortality from myocardial infarction, whereas treated systolic blood pressure (SBP) was a strong predictor. There was a J-shaped relation, confined to those with evidence of ischaemic heart disease, between frequency of death from myocardial infarction and treated DBP (phase V); the frequency was lowest at treated DBP of 85-90 mm Hg and rose with treated DBP on either side of this range.