Objective. To compare the antihypertensive effect of treatment with zofenopril vs candesartan by office and ambulatory blood pressure (BP). Design and methods. Following a 2-week wash-out from previous treatment, 236 grade I-II primary hypertensive patients were randomized double-blind to 12 weeks treatment with zofenopril 30 mg or candesartan 8 mg od. After 4 weeks, treatment was doubled in responder non-normalized (office systolic BP>140 mmHg and office diastolic BP reduction >10 mmHg) or non-responder patients (office systolic BP>140 mmHg and office diastolic BP reduction v10 mmHg). Following a further 4 weeks, non-responder or non-normalized patients were withdrawn. Results. In the intention-to-treat population, office systolic BP and diastolic BP reductions after 12 weeks of treatment were similar between the two groups (zofenopril: 21¡11/15¡8 mmHg, n5114 vs C: 20¡11/15¡7 mmHg, n5122; p5NS). In the 163 patients of the per-protocol population, office BP dropped by 22¡11/15¡8 mmHg (zofenopril) and 20¡10/15¡7 mmHg (candesartan; p5NS). Also 24-h ambulatory BPs were equally reduced by zofenopril and candesartan ( 7¡13/5¡8 mmHg vs 7¡12/5¡8 mmHg; p5NS). The trough-to-peak ratio and smoothness index were not significantly different between zofenopril and candesartan. Tolerability of both drugs was good. Conclusions. Monotherapy with zofenopril and candesartan similarly reduced office and 24-h BPs. Since almost 90% of patients were normalized by either zofenopril or candesartan, this result supports the importance of considering low-or high-dose monotherapies as initial treatment for most hypertensive patients of mild degree.