This volume of the Handbook of Experimental Pharmacology (Concepts in Biochemical Pharmacology) will show that pharma­ cology has finally arrived as a true discipline in its own right, and is no longer the handmaiden of organic chemistry and physiology. Instead it is an amalgam of all the biological sciences including biochemistry, biophysical chemistry, physiology, pathology and clinical medicine. In the volumes that make up Concepts in Bio­ chemical Pharmacology we hope to convince Medical Schools what should now be obvious, that pharmacology is no longer that dull topic bridging the basic sciences with medicine, but is probably the most important subject in the medical curriculum. We are grateful for the advice of Dr. Byron Clark, Director of the Pharmacology-Toxicology Program at the National Institutes of Health whose support made possible much of the work described in this volume. Contents Section Four: Methods 01 Stooging the MetoholiBm 01 Drugs Subsection A. Assay 01 Drugs and Their M etoholites Chapter 22 : Basic Principles in Development of Methods for Drug Assay. B. B. BRODIE. With 2 Figures 1 1 A. Introduction . . . . . . . . . . B. Principles of Developing a Method. . . . . . 1 I. Section of Method of Assay . . . . . . 1 II. Choice of Solvent for Extraction of Drug 2 III. Adsorption of Drugs by Glass Surfaces . . . . . . . . . . . . . . 3 IV. Recoveries of Known Amounts of Compound from Biological Material. 4 V. Assessment of Sensitivity 5 VI. Assessment of Specificity 5 References. . . . . . . . . . .