Abstract The effects of somatostatin, a tetradecapeptide isolated from hypothalamus extracts, were studied on the vascular reactivity of aorta and mesenteric arteries isolated from rabbits. We also investigated whether or not Ca 2+ movements were implicated in these effects. Rabbit aorta and mesenteric (fifth branch) arteries were isolated, cleaned off, and mounted in an organ bath containing Godfraind solution or physiological saline solution (PSS), respectively. Somatostatin (10 −8–10 −4 M) produced a concentration-dependent inhibition of the contractile responses induced by high K + (80 mM) or noradrenaline (10 −6 M in aorta or 10 −4 M in mesenteric arteries) in both arteries studied. The inhibitory effect of somatostatin was greater in mesenteric resistance vessels (IC 50 3.1±2.3×10 −5 M, and 5.2±4.8×10 −8 M with KCl and noradrenaline, respectively). Contractile responses produced by the addition of Ca 2+ (1–5 mM) to Ca 2+-free high K + solution were also concentration dependently inhibited by somatostatin in aorta. Furthermore, somatostatin decreased noradrenaline-induced contraction attributed to intracellular Ca 2+ release in aorta, and inhibited 45Ca 2+ uptake stimulated by high K + or by noradrenaline. However, it did not modify 45Ca 2+ uptake in resting mesenteric resistance arteries. Taken together, these results suggest that somatostatin exerts an inhibitory effect on vascular contractions induced by some stimulating agents in different arteries isolated from rabbits, being more potent in mesenteric arteries.