We reviewed the designs and major results of 17 large-scale, controlled, clinical trials that reported the effects of drug treatment for hypertension on morbidity or mortality. Seven trials conducted in study populations with more-severe hypertension (diastolic blood pressures 100-120 mm Hg or higher), including the more-severe stratum of the Veterans Administration Trial, showed large reductions in stroke, other "hypertensive" events, and, in one trial, total mortality. Of 11 trials in populations with less-severe hypertension (diastolic blood pressures predominantly below 105 mm Hg), including the less-severe stratum of the Veterans Administration Trial, nine met the criteria for pooling of results. Among the aggregate 43,000 patients in the nine trials who were followed up for an average of 5.6 years, mean diastolic blood pressure reduction was 5.8 mm Hg, and a significant 11% reduction in total mortality was observed. This benefit was largely attributable to a 38% reduction in fatal strokes; nonfatal strokes were similarly reduced. Coronary heart disease mortality was 8% lower in drug treatment than in control groups, but this difference was not significant. A similar result was observed for combined coronary mortality and nonfatal myocardial infarction. A possible explanation for the inconclusive result regarding coronary end points was an adverse trend, observed in several trials, in a subgroup with baseline resting electrocardiographic abnormalities. Because all the trials except the propranolol arm of the Medical Research Council trial used drug regimens based on thiazide-like diuretic agents, and because there are now several new drug classes proposed as initial therapy, additional large-scale clinical trials may need to be considered.