Renin classification has been proposed to guide initial treatment of hypertensive patients with diuretics vs beta-blockers. Most previous studies evaluating this issue have utilized patient populations that were white or predominantly white. Black hypertensives have been noted to differ from white hypertensives in several respects. To evaluate the clinical utility of renin classification in black hypertensives, we compared the blood pressure response of low vs normal renin patients during double-blind treatment with either hydrochlorothiazide or beta blocker (metoprolol or oxprenolol). Hydrochlorothiazide a significantly (P less than 0.05-0.01) larger blood pressure fall than beta-blocker, though there was no difference in the response of low vs normal renin patients. Thus, renin classification does not appear to guide initial selection of diuretic vs beta blocker therapy of black hypertensives, and diuretic therapy is more effective.