Radioactive tracers have had a profound impact on scientific research during the past twenty years, particularly in bio­ chemistry and allied fields. The rapid evolution of sophisticated instrumentation and labeling techniques during the past ten years has made possible on a routine basis exquisitly sensitive experiments which with other techniques would require her­ culean efforts on the part of the investigator. The Symposia on Advances in Tracer Methodology, which have been held regularly since 1957, provide for research workers in biochemistry, pharmacology, endocrinology, and medicine a focus on the numerous developments in the tracer field that are usually scattered throughout the scientific literature. Volume 3 is arecord of the proceedings of the Ninth and Tenth Symposia, which were sponsored by the New England Nuclear Corporation and the Packard Instrument Company, Inc. Recent advances in tracer methodology, as reflected by the papers in this volume, have been mainly concerned with im­ proved analytical techniques, such as liquid scintillation count­ ing, autoradiography, and chromatography, and with novel ap­ plications of labeled compounds in biochemical and clinical problems.

Preparation of Labeled Compounds.- Carbon-14- and Tritium-Labeled DPN and TPN.- Synthesis and Metabolism of Glucose-3-H3 and Glucose-4-H3.- Use of Vinyl Magnesium Bromide in the Synthesis of Labeled Compounds: New Preparations of Glycerol-1-C14 and Glyceric Acid-1-C14.- C14-Labeled Cardiac Glycosides.- A Simple Method of Preparing Labeled Benzene.- Synthesis of 35S-p-Toluene Sulfonic Anhydride (Tosan) of High Specific Activity.- The Correlation Between Structure and Tritium Incorporation During Labeling by the Wilzbach Method.- Synthesis of 32P-, 14C-, and 3H-Labeled Lecithins and Their Use in Studies on Lipid Metabolism.- Specific Analytical Techniques.- Liquid Scintillation Counting.- Improved Methods for Liquid Scintillation Assay of (a) C14-Compounds on Paper Chromatograms and (b) C14-Protein.- Quenching Correction in Liquid Scintillation Counting.- Quench Monitoring and Efficiency Calibration Through External Standardization.- Comparison of Various Procedures for the SimultaneousMeasurement of 32P and 45Ca in Inorganic Salts by Liquid Scintillation Counting.- Problems of Liquid Scintillation Counting on Studies of Metabolic Balances.- Autoradiography.- Electron Microscope Autoradiography.- A New Method of Macroautoradiography.- Thin Layer Fluorography of Tritium-Labeled Compounds.- Thin Layer Autoradiographic Electrophoresis of Tritium-Labeled Compounds in Buffered Photographic Gelatin.- Chromatography.- Concentration Profile in Paper Chromatography Investigations of a Labeled Substance.- The Importance of Isotope Fractionation in the Clinical Application of Labeled Aldosterone.- Recent Investigations on Cholesterol Metabolism: Critical Evaluation of Radiochromatography and Estimation Procedures.- Biochemical Applications.- Isotope Studies on Citrate-Condensing Enzyme.- Rapid Inhibitor-Induced Changes in the C14-Labeled Compounds Formed by the Photosynthetic Carbon Reduction Cycle.- Application of Double Isotope Labeling to the Study of the Metabolism of Ascites Tumor Cells Under the Influence of Glyceraldehyde.- Nucleic Metabolism During Antibody Synthesis in vitro.- The Biosynthesis of Prostaglandin-E1 Studied with Specifically 3H-Labeled Precursors.- The Use of Labeled Substrates in the Study of Isoprenoid Degradation.- Use of Different Isotopes in the Study of Cell Differentiation.- Clinical Applications.- Degradation of C14-Labeled Thymidine and Its Halogenated Analogues in Man.- Quantitative Measurement of Transplantation Immunity.- Studies of the Secretion and the Metabolism of Steroid Conjugates: Synthesis, Analysis and Use of Doubly Labeled Compounds.- Countercurrent Distribution Combined with Liquid Scintillation Counting of Double-Labeled Water-Soluble Radioactive Material in the Study of the Metabolism of Steroid Conjugates.- Conjugation (Detoxification) of C14-Labeled Cholic Acid in Human Liver Homogenates as a Test of Liver Function.- Health Physics.- Atmospheric Bomb Radiocarbon as a Tracer in Human Beings.