A double-blind, randomised, parallel study compared the BP and metabolic responses in black hypertensive patients following monotherapy with nicardipine or hydrochlorothiazide (HCTZ). Following a single-blind placebo wash-out period of 1-4 weeks, the study drug, nicardipine 20-40 mg three times daily or HCTZ 25-100 mg four times daily, was administered in a double-blind fashion for 12 weeks. Doses were titrated to control sitting DBP (< or = 90 mmHg). Both drugs were effective in reducing sitting SBP and DBP as compared with baseline values (nicardipine: 152.5 +/- 1.6/102.0 +/- 0.6, HCTZ: 152.5 +/- 1.5/101.4 +/- 0.5 mmHg). DBP responses (reduction from baseline; nicardipine: -10.9, HCTZ: -12.7 mmHg), and the percentage of patients achieving a response < or = 90 mmHg (nicardipine: 54%, HCTZ: 63%) to the two drugs were similar. Although SBPs at baseline and endpoint (137.3 +/- 1.6 on nicardipine and 132.1 +/- 1.4 mmHg on HCTZ), and the percentage of patients achieving a response < or = 140 mmHg (nicardipine: 70%, HCTZ: 79%), were comparable between the two treatments, the SBP reduction with HCTZ was statistically greater (P = 0.026). A comparison of the metabolic responses in the two treatment groups showed significant differences. Nicardipine caused no significant changes in blood chemistry, whereas HCTZ caused statistically significant decreases (P < 0.001) in sodium and potassium and increases (P < or = 0.01) in glucose, BUN, creatinine, uric acid, cholesterol and LDL compared with baseline. In 12.7% of the patients in the HCTZ group, serum potassium dropped to levels < 3.5 meq/l, which occurred in only 1.4% of the patients who used nicardipine.(ABSTRACT TRUNCATED AT 250 WORDS)