The leucoyte surface antigen CD38 has been shown to be an ecto-enzyme with multiple catalytic activities. It is principally a NAD ⁺ glycohydrolase that transforms NAD ⁺ into ADP-ribose and nicotinamide. CD38 is also able to produce small amounts of cyclic ADP-ribose (ADP-ribosyl cyclase activity) and to hydrolyse this cyclic metabolite into ADP-ribose (cyclic ADP-ribose hydrolase activity).