Marijuana is used by humans for its psychoactive and medicinal effects. The active constituents of marijuana, the cannabinoids, exert effects via a G protein-coupled receptor, CB(1). Two arachidonic acid analogs, N-arachidonylethanolamine and 2-arachidonylglycerol are hypothesized to function as endogenous ligands of the CB(1) receptor. The cannabinoids exert significant vascular effects in humans and laboratory animals. In particular, the cannabinoids produce vasodilation and hypotension. The possible mechanisms for these effects are inhibition of transmitter release from sympathetic nerve terminals, direct effects on vascular smooth muscle cells, and effects on endothelial cell function. The data regarding these effects of the cannabinoids and possible sources of endocannabinoid ligands in the vasculature are the subjects of this review.