The blood pressure-lowering properties of lyophilized chokeberry juice and polyphenols were monitored using in vitro angiotensin-converting enzyme (ACE) inhibition measurement and a 10day in vivo study with spontaneously hypertensive rats (SHR). Juice and polyphenols indicated weak ACE-inhibitory activity. The IC 50 values for polyphenols and juice were 1.5–2.5 and 4.5mg dry matter/ml, respectively. In the SHR study the blood pressure-lowering effects of juice and polyphenol extract seemed to be short-term and were generally highest after 3h from administration (50mg/kg/day) when mean reductions in systolic blood pressure were 20±8 and 15±7mmHg, respectively. Corresponding mean decreases in diastolic blood pressure were 23±6 and 13±2mm Hg in juice and polyphenol groups, respectively. It was concluded that both chokeberry juice and polyphenols had blood pressure-lowering effects. We hypothesize that chokeberry polyphenols enhance endothelial nitric oxide production with an ACE-independent mechanism, e.g. by activation of endothelial nitric oxidase enzyme; this is yet to be verified.