Cyclic ADP-ribose (cADPR) is a novel endogenous metabolite of nicotinamide adenine dinucleotide (NAD⁺), and is a recently discovered second messenger. cADPR is active in mobilizing intracellular Ca²⁺ in invertebrate as well as mammalian cells. The mechanism of releasing Ca²⁺ from internal pool (s) has been studied. cADPR may bind its receptor, which in turn induces the release of Ca²⁺ from cADPRsensitive Ca²⁺ pool(s) through ryanodine receptor or ryanodine receptor-like mediated Ca²⁺ channel. In addition,a possible intracellular signal transduction pathway involving nitric oxide(NO)，cyclic guanylic acid(cGMP ) and cADPR has been suggested to exist in various cells.