Peroxynitrite-induced oxidative stress was investigated in red blood cells by luminol-dependent chemiluminescence. Red blood cells are susceptible to free radical damage due to the abundance of oxygen, presence of iron and other agents such as polyunsaturated fatty acids. Peroxynitrite (ONOO-), formed by the reaction of superoxide radical with nitric oxide radical, has been shown to cause protein and lipid oxidation. Addition of ONOO- showed a dramatic increase in chemiluminescence, but treatment with glutathione ethyl ester, an antioxidant, partially reduced the increase in chemiluminescence. The results show that red blood cells are a good model to mimic oxidative stress conditions and are discussed with relevance to neurodegenerate disorders.