5,5-dimethyl-1-pyrroline-N-oxide (DMPO), a highly reactive and short-lived compound, which is a commonly used as a spin trap that reacts with radicals. It can control intracellular nitroso-redox balance by scavenging ROS and donating NO. Experiments with bovine aortic endothelial cells have shown that post-treatment with DMPO of oxidatively challenged cells reversed eNOS dysfunction and could have pharmacological implications in the treatment of cardiovascular diseases. Besides DMPO can reacts with the amino acid- and DNA base-derived radicals to form protein- and DNA-DMPO nitroxide radical adducts, respectively. These adducts then decay to form very stable product macromolecule-DMPO-nitrone and can be detected by mass spectrometry, NMR or immunochemistry by the use of anti-DMPO nitrone antibodies. Thus Anti-DMPO antibodies can be used to determine the distribution of free radicals in cells and tissues and even in living animals and this may have a main role for the understanding the role of free radicals in biochemistry, medicine, and toxicology.