This multicenter, randomized, double-blind, parallel group study was undertaken to determine the effectiveness of selected antihypertensives (doxazosin, amlodipine, enalapril, and bendrofluazide) in maintaining 24-hour control of blood pressure (BP). The predictive value of ambulatory (A)BP versus clinic (C)BP measurements as a method for detecting patients with hypertension was also evaluated. A total of 204 patients were screened and of these 110 were diagnosed as mild to moderately hypertensive with clinic diastolic BP 100–110 mm Hg (≧95 mm Hg in patients with coronary heart disease risk factors). The 4 antihypertensives were all equally effective at controlling BP over 24 h, as shown by 24-hour ABP measurements. The incidence of adverse events was similar for all 4 treatment groups; headache was the most common event, being reported by 22 patients (20%). There was a clinically relevant reduction in total cholesterol for the doxazosin (–15.4 mg/dl) and amlodipine (–11.6 mg/dl) treatment groups in comparison with enalapril and bendrofluazide. Our results from ABP measurements suggest that the antihypertensives studied are effective first-line therapy in the regulation of hypertension and that ABP is a reproducible measure. ABP may also be useful in identifying patients with various types of high BP, for instance those with ‘white coat’ hypertension, enabling more accurate screening and diagnosis.