Background and purpose: A putative novel cannabinoid receptor mediates vasorelaxation to anandamide and abnormal-cannabidiol and is blocked by O-1918 and by high concentrations of rimonabant. This study investigates VSN16, a novel water-soluble agonist, as a vasorelaxant potentially acting at non-CB , non-CB cannabinoid receptors in the vasculature. Experimental approach: VSN16 and some analogues were synthesized and assayed for vasodilator activity in the rat third generation mesenteric artery using wire myography. Also carried out with VSN16 were haemodynamic studies in conscious rats and binding studies to CB receptors of rat cerebellum. Key results: VSN16 relaxed mesenteric arteries in an endothelium-dependent manner. The vasorelaxation was antagonized by high concentrations of the classical cannabinoid antagonists, rimonabant and AM 251, as well as by O-1918, an antagonist at the abnormal-cannabidiol receptor but not at CB or CB receptors. It did not affect [ H]CP55,940 binding to CB receptors in rat cerebellum. The vasorelaxation was not pertussis toxin-sensitive but was reduced by inhibition of nitric oxide synthesis, Ca -sensitive K channels (K ) and TRPV receptors. In conscious rats VSN16 transiently increased blood pressure and caused a longer-lasting increase in mesenteric vascular conductance. Structure-activity studies on vasorelaxation showed a stringent interaction with the target receptor. Conclusions and implications: VSN16 is an agonist at a novel cannabinoid receptor of the vasculature. It acts on the endothelium to release nitric oxide and activate K and TRPV . As it is water-soluble it might be useful in bringing about peripheral cannabinoid-like effects without accompanying central or severe cardiovascular responses. © 2007 Nature Publishing Group All rights reserved.