The development of neurophysiology, the study of the activity of living nervous tissue, has relied heavily on the techniques of electrophysiology. This emphasis is revealed in volumes 14 and 15 of this series, which show how electrophysiological techniques can be applied to research topics ranging from ion channels to human behavior. Kitai and Park show how cellular neurophysiology can be related to classical neuroanatomy, an important basis for any type of functional analysis. Wonderlin, French, Arispe, and Jones describe new (single channel) and more traditional (whole cell) techniques for studying the role of ion channels in cellular pr- esses, a field that is currently developing very rapidly. An exciting nontraditional approach to the study of cellular electrophysiology is discussed by Hopp, Wu, Xiao, Rioult, London, Zecevic, and Cohen in their paper on optic measurement of membrane pot- tials. Humphrey and Schmidt offer a thoughtful review of the uses and limitations of the technique of recording extracellular unit potentials in the brain. Hoffer presents an introduction to a field that is of great interest but is technically very difficult-the reco- ing from cells and axons in the spinal cord and peripheral nervous system in freely moving animals. An electrophysiological approach to the analysis of the neural mechanisms of normal behavior is presented by Halgren in a wide-ranging review of the field of evoked potentials in humans.