Nebivolol is a highly selective β 1-adrenoreceptor-blocking agent with a peculiar pharmacodynamic profile. It has peripheral acute vasodilating properties that are mediated by modulation of the endogenous production of nitric oxide. In this study we analyzed the different signaling pathways implicated in the response of human umbilical vein endothelial cells to nebivolol. Its effect on endothelial transduction pathways was determined by assaying phospholipase C and A 2 activities and cyclic adenosine monophosphate (AMP) production. Variations in intracellular calcium concentration were also measured. Our results showed that nebivolol activates a calcium-independent transduction pathway that implicates an increase in adenylate cyclase and phospholipase A2 activity. β 1-or β 2-Adrenoreceptor antagonists do not inhibit the action of nebivolol. However, its action on cyclic AMP production is inhibited by bupranolol, a β 1-3-adrenoreceptor antagonist, and S-(-)-cyanopindolol, a selective β 3-adrenoreceptor antagonist. Nebivolol also dose-dependently increased nitrite production. This effect was inhibited by bupranolol, suggesting that the possible action of nebivolol on β 3-adrenoreceptor is involved in its vasodilating properties. This study suggests that nebivolol could behave as a β 3-adrenoreceptor agonist and induce some calcium-independent pathways implicating phospholipase A 2 and adenylate cyclase. This agonistic activity of nebivolol seems to be responsible for its endothelium-dependent vasodilating activity.