CB2cannabinoid receptor-selective agonists are promising candidates for the treatment of pain. CB2receptor activation inhibits acute, inflammatory, and neuropathic pain responses but does not cause central nervous system (CNS) effects, consistent with the lack of CB2receptors in the normal CNS. To date, there has been virtually no information regarding the mechanism of CB2receptor-mediated inhibition of pain responses. Here, we test the hypothesis that CB2receptor activation stimulates release from keratinocytes of the endogenous opioid-endorphin, which then acts atopioid receptors on primary afferent neurons to inhibit nociception. The antinociceptive effects of the CB2receptor-selective agonist AM1241 were prevented in rats when naloxone or anti-serum to-endorphin was injected in...