Aim To study the vasodilation of MS23,a brand new phosphodiesteras inhibitor,on contractions induced by various stimuli in rings of arteries isolated from rat different organs.Method Tension of aortic and microvessel rings were recorded isometrically by PowerLab and DMT system respectively.Results MS23 concentration-dependently shifted the noradrenaline(NA)-induced concentration-contraction curves rightward in a non-parallel manner with the maximal contraction depressed by 74.7%.MS23 and aminophylline(Ami) produced concentration-dependent relaxation on KCl or NA-induced precontraction.Endothelium deprivation and NO synthesis inhibition induced by L-NAME failed to affect the relaxation.MS23 and Ami relaxed KCl-induced precontraction of rat coronary,middle cerebral,renal and mesenteric arterial rings in a concentration-dependent manner,and showed no organ preference in this respect.Conclusion MS23 antagonizes and relaxes contractions induced by various stimuli in the rings of arteries isolated from different organs of rat without marked preference among the organ origin of artery and stimuli.The vasorelaxation induced by MS23 is related neither to endothelium nor to nitric oxide synthesis.