CYPMPO is a free radical spin trap with excellent trapping capabilities toward hydroxyl and superoxide radicals in biological and chemical systems.{14615} Decay of the superoxide adduct of CYPMPO proceeds in an apparent first order fashion with half-lives of 15 and 51 minutes in a UV-illuminated hydrogen peroxide solution and a hypoxanthine/xanthine oxidase system, respectively. CYPMPO traps superoxide radicals generated by bovine neutrophils as effectively as DEPMPO.{14615} The high melting point (126°C), low hygroscopic properties, and long shelf-life in aqueous solutions offer significant practical advantages for use of CYPMPO over DEPMPO and DMPO.