Medicinal products are important in the prevention, diagnosis and treatment of diseases and considerable resources are invested in their invention and development. The advent of new biochemical techniques has greatly increased our understanding of the molecular processes taking place in living organisms and has also created the possibility for their manipulation. These developments have already led to the production of many novel medicinal products and many more are being developed. This text is designed to provide insight and information in how modern biotechnology may be applied to produce useful medicinal products by drawing on industry's experiences to date. In the development of new medicinal products both the process of development and licensing procedures play an important role, and therefore both have aspects dealt with in this text, which outlines the whole route from the initiation of the development of a new product to the granting of a marketing licence. The text is divided into two parts - an introductory part and a series of case studies, starting with a general introduction of modern biotechnology, summarizing its historical development, the possible role of modern biotechnology in the healthcare business and its impact on society. This is followed by a chapter describing the stages involved in developing and producing a new medicinal product. The introductory part concludes with a chapter that describes the general elements that a licensing file of a biotechnological medicinal product should contain. The introductory part is followed by a number of case studies, selected to provide the reader with a breadth of experience. The structure of each case study is based upon the sequences of activities undertaken to produce a new product. The case studies include therapeutics (insulin, erythropoietin and orthoclone OKT3), vaccines (hepatitis B, Aujeszky's disease) and diagnostics (myoscint, Aujesky's disease). The concepts and issues discussed in this text are quite advanced. The emphasis is on application of biotechnology, rather than on the principles of the methods of biotechnology. It is assumed that the reader has a basic understanding of restriction enzymes and genetic manipulation procedures and of the principles underpinning cell fusion (hybridoma) technology. Since many of the products discussed are derived from or have an effect on the immune system, a basic knowledge of the processes of immunity will be helpful. Self assessment questions within this text assume a working knowledge of these techniques. Specialized techniques however are explained in appropriate places.