This small volume consists of 22 papers read at a symposium in London in March, 1951. Each paper concludes with a résumé of the discussion that followed its reading. The symposium was attended by 78 leading isotope experts, about half of them from Great Britain, with representation from other European countries, the United States, Canada, and South America. The subject matter of the book is divided into six sections: (1) steroids, (2) hemoglobin and metabolic derivatives, (3) the use of tracers in the study of biologic effects of radiation, (4) nucleic acids, (5) proteins and amino acids, and (6) carbohydrate and fatty acid metabolism. These topics are reviewed in detail, the book being useful primarily to research workers in the isotope field or others contemplating the use of these techniques in their research. There is little to interest general practitioners, except those seeking an authoritative summary of actual biochemical investigations