This book is concerned with protein metabolism at the physiological, not the molecular level and particularly with studies on human beings. Protein turnover is a vital function, no less important than oxygen turnover, because of this over the last 20 years there has been an increase in the research on protein turnover in man, with parallel work on farm animals. Methods that have been used for measuring whole body protein turnover in man, the underlying problems and assumptions and the problems that have been encountered are discussed in this comprehensive book.