There is currently limited acceptance of foreign clinical data by regulatory authorities, although the reasons for repeating studies are poorly defined. There are some proven genetic differences in drug metabolism and elimination which occur with varying frequencies in different populations. In addition, there are differences in culture, environment and medical practice which can impact on drug reponsiveness. This book, a further edition in the CMR Workshop Series, reviews the proceedings of a workshop held in London in July 1993 to address these issues. The contributors review the current situation, address the scientific basis for repeating clinical trials in different ethnic groups, consider specific examples, and assess the relevance of interethnic and environmental differences in responsiveness for drug development.