This article reviews the evidence on pharmacologic therapy of hypertension in reducing morbidity and mortality from stroke and coronary heart disease (CHD) and considers the possible generalizability of these findings to diabetics. For malignant hypertension, benefits are large and obvious from uncontrolled case series. For severe hypertension, conclusive benefits have been shown in several randomized trials. For mild to moderate hypertension, however, it is necessary to consider meta-analyses of all individual trials. The most comprehensive of these shows reductions of 42% for total stroke (95% Cl, -33 to -50%; P < 0.0001) and 14% for all CHD (95% Cl, -4 to -22%; P < 0.01). The applicability to diabetics is unclear because they were excluded from most of the trials. The Hypertension Detection and Follow-Up Program included diabetics and reported subgroup analyses. The reduction in mortality among the actively treated diabetics of 5% was less than the 17% achieved in nondiabetics. It is unclear, however, whether the mortality reductions are truly different or reflect the play of chance. Because of the higher incidence of CHD events among diabetics with hypertension, a similar relative benefit would result in a much greater absolute risk reduction. Further, the drugs used adversely affect lipid and glucose metabolism. New antihypertensive drugs without these side effects may further improve the risk-to-benefit ratio of antihypertensive treatment, especially in diabetics, who are at a several-fold absolute increased risk or cardiovascular disease.(ABSTRACT TRUNCATED AT 250 WORDS)