While serendipity and random screening continue to fulfil a significant role in the search for new drugs, current remarkable advances in molecular biology and genetics are dictating to a profound extent the approaches employed in their development. Increasing attention is being devoted to investigations of the mechanisms of action of existing drugs, and the sources of undesired side effects, at the molecular level. The information so derived is now extensively applied, with the aid of broad inter disciplinary approaches, both theoretical and experimental, to improvements in existing drugs,...