This third edition of Basic Pharmacology retains the overall objectives of the first. It aims to present accounts of drug actions and their mechanisms in a compact, inexpensive and up-to-date form. The book is therefore designed to help students of subjects allied to medicine to appreciate the rationale underlying the uses of drugs in therapeutics. The book is divided into sections. Each section follows a particular theme and is introduced by the relevant pharmacological general principles. Prompts to revise the relevant anatomical, biochemical or physiological concepts and data are also given. In each section, the major groups of drugs relevant to the theme are discussed with detailed expositions of the important type substances. Drugs of lesser importance are placed in proper context. Two key themes dominate the text. Selectivity (that is, the ability to chemically influence one kind of biological activity without modifying another) is the central theme of pharmacology. Such selectivity is relative, rather than absolute. This places the onus of responsibility for safe usage firmly on the intending exploiter of the properties of drugs. The principal changes that this third edition of Basic Pharmacology shows from the second are: updating (as of 1990) of the accounts of mechanisms of drug action; updating (after British National Formulary (BNF) 1990, Number 20) of the selection of drugs for discussion; movement of the section entitled General Pharmacology from last to first position; expansion of the chapters on adverse drug interactions, cardiac antidysrhythmic drugs, calcium channel blockers, local hormones and chemotherapy of bacterial infections; and the provision of new chapters on allergically determined hypersensitivity to drugs.