OXYGEN IS ESSENTIAL TO NORMAL BRAIN FUNCTION, but sometimes, like Kentucky bourbon, too much of a good thing is detrimental. In particular, reactive oxygen species (ROS) and reactive nitrogen species (RNS), although important in neuronal signaling and physiology at low levels, can, at higher levels, lead to neuronal dysfunction and death (4). Some aspects of free radical chemistry applicable to brain are discussed here and in the contributions of this Forum that follow. It is the opinion of this Forum Editor that this collection of comprehensive and thought-provoking reviews and primary data articles will be of immense value to scientists and physicians involved in research in and/or care of persons with neurodegenerative disorders. Principles outlined here may be applicable to other neurodegenerative disorders not discussed in this forum. As Forum Editor, I take responsibility for the choice of persons invited to participate and topics covered in this Forum but credit for only the research in my own Forum Review article. I am truly grateful to the outstanding scientists and physicians who have contributed to this exceptional collection of articles.