Adalat (R) OROS, a controlled-release formulation for once-a-day administration, was evaluated in the Modern Approach of the Treatment of Hypertension (MATH) trial. In this study conducted at 127 centers, 1155 patients with mild to moderate hypertension representative of the spectrum seen in practice were included in the analyses of effectiveness. After a 2 week placebo period, Adalat (R) OROS therapy was started at 30 mg/day and was titrated to a maximum dose of 180 mg/day over 6 weeks. Response criteria were a sitting diastolic blood pressure < 90 mm Hg and a decrease of > 10 mm Hg. After titration, patients were observed for 12 weeks during treatment. At the final visit, Adalat (R) OROS significantly (P < 0.0001) reduced sitting systolic blood pressure 17 +/- 14 mm Hg < mean +/- SD), and sitting diastolic blood pressure 14 +/- 8 mm Hg. Similar highly significant reductions in standing blood pressure were observed. For all subjects, 76% achieved goal blood pressure response during titration. More than 50% were controlled on doses of 30 to 60 mg/day. At the final visit blood pressure reductions in men and woman were similar, except for a significantly greater decrease in sitting systolic pressure for women. A similar proportion of blacks responded compared with whites, and reductions in sitting systolic and diastolic blood pressure were also similar in the 2 groups. Adalat (R) OROS had no effect on renal function, serum potassium, or total, HDL-, or LD- cholesterol. Uric acid was reduced by 0.5 mg/dL (P < 0.0001). Edema was the most common complaint and was dose-related; < 10% of patients were discontinued from treatment for this symptom. Adalat (R) OROS is effective, and well tolerated monotherapy for mild-to moderate hypertension as usually encountered in medical clinics and practices.