ERM (Ezrin, Radixin & Moesin) proteins are known to be linkers between the actin cytoskeleton and membrane proteins. We have investigated the activation of these proteins in intact rat aorta by using a phospho-ERM antibody and Western-Blot technique. Stimulation with noradrenaline (1mM) rapidly increased ERM phosphorylation, which was maximum at 2 min and slightly decreased at 10 min. ERM proteins were also phosphorylated by 100 mM KCl stimulation with a maximal phosphorylation after 30 s and a fast decrease after longer stimulation, indicating that ERM proteins can be phosphorylated by different pathways. The inhibitor of Rho kinase (Y27632 10 mM), totally inhibited ERM phosphorylation measured after 2 and 10 min of noradrenaline stimulation but did not affect the rapid increase (30 s) in ERM phosphorylation induced either by noradrenaline or high KCl. The rapid increase in ERM phosphorylation induced by KCl stimulation was completely inhibited by 1 mM nimodipine, a blocker of voltage-gated calcium channels. Furthermore, ionomycin, a calcium ionophore, induced a rapid increase in ERM phosphorylation. Moreover, GÖ6983, an inhibitor of calcium-activated PKC, totally inhibited the fast ERM phosphorylation evoked either by noradrenaline or KCl stimulation but not the phosphorylation induced by a longer stimulation with noradrenaline. These results indicated that ERM proteins were phosphorylated in vascular smooth muscle in response to agonist or depolarising stimulation. This phosphorylation consisted in two different phases: a fast calcium dependent phosphorylation induced by PKC and a much slower calcium independent phosphorylation induced by Rho kinase.