2,2,6,6-Tetramethylpiperidin-1-oxyl (TEMPO) is a stable radical that will react with reactive oxygen species (ROS). This conversion, followed by ESR, provides an indirect way to monitor ROS production in biological systems. TEMPONE is the 4-oxo derivative of TEMPO. In addition to possible uses as a spin trap, this nitroxyl radical can be used in hydrogen transfer experiments and as a polarizing agent in dynamic nuclear polarization NMR spectroscopy. TEMPONE and other nitroxyl radicals have also been shown to reduce mean arterial pressure in spontaneously hypertensive rats when administered intravenously.