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 Bioche mical 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 CLARKE, Director of the Pharmacology-Toxicology Program at the National Insti tutes of Health, whose support made possible much of the work described in this volume. Contents Section One: Routes of Drug Administration Chapter 1: Biological Membranes and Their Passage by Drugs. C. A. M. HOGBEN 1 References… … … … … … … … . . 8 Chapter 2: Absorption of Drugs from the Gastrointestinal Tract. L. S. SCHANKER. With 5 Figures. 9 I. Introduction… … … … … … … . . 9 II. Methods of Study… … … … … … … 9 III. Absorption from the Stomach … … … … … 11 IV. Intestinal Absorption of Non-Electrolytes and Weak Electrolytes 15 V. Absorption of Weak Electrolytes from the Colon and Rectum 18 VI. Intestinal Absorption of Organic Ions… … … . 19 VII. Intestinal Absorption of Macromolecules … … … . 19 VIII. Active Transport across the Intestinal Epithelium … . . 20 IX. Effect of EDTA on Drug Absorption from the Intestine … … .