Elastin peptides are present in human blood. As elastin receptors exist on several cell types, especially endothelial cells, this investigation was carried out to study the effect of elastin peptides on vascular tone. For this purpose, rat aortic rings were mounted in an organ bath for isometric tension measurements. Elastin peptides (ĸ-elastin) were added in the concentration range of 0.1 ng/ml to 1 µg/ml, concentrations similar to those found in the circulating blood. In rat aortic rings, precontracted or not with noradrenaline (10<sup>–6</sup> M), elastin peptides induced an endothelium-dependent vasodilation. The pretreatment of aortic rings with N-ω-nitro- L-arginine methyl ester (10<sup>–5</sup> M), an inhibitor of nitric oxide (NO) production, or with indomethacin (10<sup>–5</sup> M), an inhibitor of cyclooxygenase, prevented elastin peptide-induced vasodilation. These findings suggest that elastin peptides act through the synthesis of prostanoids, leading to the production of NO. Moreover, this relaxant effect of elastin peptides was decreased or inhibited when aortic rings were treated with lactose (10<sup>–5</sup> to 10<sup>–2</sup> M) or laminin (10<sup>–6</sup> to 10<sup>–4</sup> mg/ml) whereas lactose or laminin was unable to inhibit acetylcholine-induced vasodilation. These findings suggest that the inhibitory effects of lactose and laminin are specific for elastin peptide receptors and are in agreement with previous studies on these receptors. As there is evidence of the degradation of elastin in several vascular diseases, the concept that elastin peptides may contribute to the control of vascular tone is discussed.