In animal arteries cannabinoids induce vasorelaxation through mechanisms that are influenced by both the cannabinoid ligand, the artery used and species studied. In human arteries the potential vascular effects of cannabinoids have not been fully investigated. The aim of the present study was to investigate the effects of a range of cannabinoids in human mesenteric arteries. With ethical approval and written informed consent, human mesenteric arteries were taken from patients receiving colorectal surgery. Arteries were dissected from mesenteric tissue, mounted on a Mulvany-Halpern myograph and bathed in oxygenated physiological saline solution (PSS) at 37°C under a set tension of 90% of 100 mmHg. Arteries were contracted and concentration response curves were carried out to anandamide (AEA), 2-arachidonyl-glycerol (2-AG), Δ-9 tetrahydrocannabinol (THC), cannabidiol (CBD), CP55,940 and HU-308. In some experiments, cannabinoid mechanisms of action were probed pharmacologically. Cannabinoid maximum responses (Rmax) were derived using mean percentage vasorelaxation data that was fitted to sigmoidal slopes using GraphPad Prism software. Comparisons between Rmax values were made using 1-way ANOVA with Bonferroni post-hoc test. Comparisons between concentration response curves in the presence or absence of pharmacological inhibitors were made using 2-way ANOVA, P<0.05 was taken as significant. With the exception of HU-308, all cannabinoids caused significant vasorelaxation of human mesenteric arteries (Rmax: AEA≈30%, 2-AG≈40%, THC≈25%, CBD≈40%, CP55,940≈55%, n=12). CP55,940 was the most efficacious cannabinoid tested with a higher Rmax than AEA (P<0.001), 2-AG (P<0.01), THC (P<0.001) and CBD (P<0.001). 2-AG was the most efficacious endocannabinoid tested causing greater vasorelaxation than AEA (P<0.05). CBD was the most efficacious phytocannabinoid tested causing greater vasorelaxation than THC (P<0.05). 2-AG-induced vasorelaxation was inhibited by COX inhibition (P<0.001, n=8), prostanoid receptor antagonism (EP4 P<0.01, n=6 & IP P<0.001, n=9), in arteries that were contracted using high K+ PSS (P<0.001, n=8) and arteries that were bathed in Ca2+-free PSS (P<0.01, n=7). Experiments probing the action of CBD revealed that vasorelaxation was dependent on CB1 (P<0.001 n=8) and TRPV1 (P<0.001, n=7) receptor activation, nitric oxide production (P<0.001, n=6), the endothelium (P<0.001, n=8) and ion channel modulation (P<0.001, n=5). AEA-induced vasorelaxation was inhibited by CB1 receptor antagonism (P<0.001, n=7), endothelium removal (P<0.01, n=6), nitric oxide inhibition (P<0.001, n=6) and inhibition of a novel, as yet uncharacterised, endothelium bound cannabinoid receptor (P<0.001, n=6). This study shows that cannabinoids cause vasorelaxation in human mesenteric arteries and therefore suggests that the endocannabinoid system may modulate vascular tone humans.