Arachidonic acid ethanolamide (anandamide) is a brain constituent that binds to the brain cannabinoid receptor (CB1). It produces many of the pharmacological effects caused by delta 9-tetrahydrocannabinol (delta 9-THC) in mice. Anandamide parallels delta 9-THC in its specific interaction with the cannabinoid receptor and in inhibition of adenylate cyclase. Two additional fatty acid ethanolamides that bind to the cannabinoid receptor, homo-gamma-linolenylethanolamide and docostetraenylethanolamide, have been identified in the brain. We believe that the anandamides are involved in the coordination of movement and short term memory. Depression of ambulation in an open field and the analgetic response to anandamide are not fully developed until adulthood, possibly due to an age-related increase in the CB1 receptor concentration. This observation has clinical implications in pediatrics. A second cannabinoid receptor (CB2) is present in the spleen. A monoglyceride, 2-arachidonyl-glycerol which binds to both CB1 and CB2 in transfected cells and inhibits andenylate cyclase in spleen cells was found in the gut. Its role is apparently associated with the immune system. These fatty acids amides and esters represent a new family of chemical modulators in the body.