BACKGROUND: Ropivacaine is a new amino ethylamide which was developed as a less cardiotoxic and long lasting local anesthetic. The local anesthetics relax bronchial and intestinal smooth muscles. In addition, most local anesthetics cause arterial dilation. METHODS: The ability of ropivacaine to elicit a relaxant effect and it's relationships with vascular endothelium and nitric oxide have been studied using isolated rat thoracic aortic rings contracted with phenylephrine (PE). Each ring of thoracic aorta was suspended on wire supports in a 20 ml tissue bath under 2 g of resting tension. All tissues were bathed in Tris Tyrode solution at 37oC and 100% oxygen was supplied. RESULTS: Ropivacaine 10-5 M inhibited PE induced contractions of aortic rings significantly (P <0.05). Relaxation effect of ropivacaine 10-5 M was recovered in denuded tracheal rings significantly (P <0.05). Relaxation effect of ropivacaine 10-5 M was recovered with L-NAME pretreatment. Ropivacaine 10-5 M inhibited both the influx of extracellular Ca2+ and intracellular Ca2+ release. CONCLUSIONS: From the results obtained with this experiments, it is concluded that the relaxation effects of ropivacaine are related with endothelium dependent and NO related. Ropivacaine inhibited both intracellular calcium release and extracelluar calcium influx.