Aliskiren (Novartis) is a new antihypertensive drug which acts by binding to the protease Renin and inhibits the conversion of Angitensinogen to Angiotensin I.. It is hoped to prevent the incomplete blockade of the Renin-Angotensin- Aldosterone system by AT1-antagonists (sartane- sensitive). Vascular smooth muscle strips were prepared for measurement of mechanical activity using organ bath techniques. Alisikiren was tested on spontaneous activity, high potassium activation (K+40mM) and Vasopressin (3 nM). Vasopressin activated A. iliaca, aorta from rat relaxed slightly on Aliskiren (10 – 50 mM). In portal vein tone slightly increased. Using high potassium activation, Aliskiren induced a further small increase of tone (1-10 mM) and an inhibition in iliac artery and aorta at higher concentrations used (30 – 50 mM). Integral of spontaneous activity of rat portal vein was increased by 30 % and the frequency was three- fold after Aliskiren treatment (1-50 mM). It is concluded, that Aliskiren exerts vasoactive affects on isolated vascular smooth muscle especially on the rhythmicity of spontaneous active tissues which might be important in the microcirculatory system, where vasomotion is an important feature.