Since the publication of the second edition of Free Radicals in Biology and Medicine in 1989 the techniques of modern molecular, cellular, and structural biology have provided new data that have transformed scientific thinking about topics within free radical research. Reactive species, such as peroxynitrite, have been discovered to have a role in biological systems. Therefore much of the third edition has been completely rewritten and what remains from the second has been thoroughly updated. There are new chapters on antioxidant defence systems in bacteria, plants, and animals; the detection of free radicals; the role of antioxidants in ageing, nutrition, disease, and therapy; and a new appendix on molecular biology. The chapter on oxidative stress and its consequences includes the damage and repair of DNA, proteins, and lipids, cytokines, and cell death (both apoptosis and necrosis). Free radicals and other reactive species are now implicated in a wide range and number of diseases and the third edition covers their role in hypertension, diabetes, lung damage, cystic fibrosis, nervous system disorders, viral infections, and cancer. This book is intended for postgraduate researchers, academics, industrial scientists, clinicians, and medical workers in chemistry, biochemistry and biomedical fields.