The effects of nitric oxide donors sodium nitroprusside and nitroglycerin on the contractile activity of the skinned rat portal vein were investigated. The skinned strips of rat portal vein were prepared by treatment 0.1 mg/ml saponin for 20 min. Maximally pCa 4.0 activated strips were exposed to nitric oxide donors. Both sodium nitroprusside and nitroglycerin induced dose-dependent decrease of the isometric force of the contraction. The inhibitor of soluble guanylyl cyclase methylene blue (50 microM) did not blocked this effect. This result shows the existence of the mechanism of NO actions on vascular smooth muscle which is not associated with the changes of intracellular Ca2+ and the activation of the soluble guanil cyclase.