The Hypertension Optimal Treatment (HOT) study showed that substantial reductions in blood pressure and a corresponding lowering of the risk of myocardial infarction could be achieved by intensive antihypertensive therapy. A cost-effectiveness analysis was performed to determine the possible economic consequences of three different targets of diastolic blood pressure lowering--< or = 90 mm Hg, < or = 85 mm Hg, and < or = 80 mm Hg, and of the coadministration of aspirin. The cost of each drug was first estimated at high and low dosage. Next, by drawing on data from the HOT trial, the mixture and dosage of drugs for each level of blood pressure control were estimated. This allowed computation of the annual cost of drugs for each blood pressure target. Because the rate of myocardial infarction (MI) was the only endpoint that differed significantly among the three target blood pressure groups, the MI risk data were converted into years of life gained on the basis of fatalities from MI averted. The cost-effectiveness ratios, expressed as cost per year of life gained, were most favorable for the < or = 90-mm Hg treatment target group ($4262) and for added aspirin treatment ($12,710). For moderately aggressive treatment (blood pressure < or = 85 mm Hg), the cost-effectiveness ratio escalated incrementally to $86,360 and with intensive treatment to $658,370 per year of life gained. Thus treatment to a target of 90 mm Hg and coadministering aspirin were considered highly cost effective, whereas treatments to lower the blood pressure further to 85 mm Hg were marginally cost effective; intensive blood pressure lowering down to 80 mm Hg was not cost effective.