The present study was aimed at investigating whether, beside its pivotal role in Ca²⁺ independent contraction of smooth muscle, Rho-kinase is involved in the mechanisms underlying the Ca²⁺ signal activated by noradrenaline in arteries. In rat aorta and mesenteric artery, the Rho-kinase inhibitor Y-27632 (10 µM) completely relaxed the contraction evoked by noradrenaline (1 µM) and simultaneously inhibited the Ca²⁺ signal by 54 ± 1 % (mesenteric artery) and 71 ± 15 % (aorta), and the cell membrane depolarisation by 56 ± 11 % (mesenteric artery). Similar effect was observed in arteries contracted by AlF4^-, while in KCl-contracted arteries, Y- 27632 decreased tension without changing cytosolic Ca²⁺. The same effects were observed with another inhibitor of Rho-kinase (HA1077) but not with an inhibitor of protein kinase C (Ro-31-8220). Effects of Y- 27632 were not prevented by incubating the artery in 25 mM KCl, with K⁺ channel blockers or with the Ca²⁺ channel blocker nimodipine. Y-27632 did not affect either the increase in the production of inositol phosphates activated by noradrenaline, or the release of Ca²⁺ from non-mitochondrial stores evoked by InsP3 in permeabilised aortic cells, or the Ca²⁺ signals evoked by thapsigargin or by caffeine. The capacitative Ca²⁺ entry activated by thapsigargin was not impaired by Y-27632 but the entry of Ba²⁺ activated by noradrenaline in the presence of nimodipine was blocked by 10 µM Y-27632. These results indicate that Rho- kinase is involved in noradrenaline-activation of a Ca²⁺ entry distinct from voltage- or store- operated channels in rat arteries.