More than for any other volume of the Handbook of Neurochemistry, the chapters in this volume on Pathological Neurochemistry deal with the interface of the laboratory bench with the patient's bedside. Most of the chapters reflect the confluence of basic scientists, clinical investigators, and physicians. Con­ sidered here are many of the more important disorders that afflict the nerves, muscles, spinal cord, and/or brain of mankind throughout the world. There are well over 500 such disorders. And our understanding of their nature and of measures for effective prevention or treatment depends significantly on appli­ cation of the biochemical disciplines that characterize neurochemistry. Before World War II, any attempt to compile a volume on pathological neurochemistry would have been largely descriptive and very rudimentary, as such "handbooks" by Hans Winterstein (1929), Irvine Page (1937), and others demonstrate. But thanks to the many major advances in research and technology in the postwar decades, we now stand at the threshold of understanding how to manage many of the major neurological disorders, and we may expect more such delineations in the immediate decades ahead. Neurochemistry, de­ fined broadly, has played a central role in this extraordinary turn of events, progressing from what J. L. W, Thudichum in 1884 called objects of anxious empiricism to his anticipation of the proud exercise of chemical precision.