More then 20 years have passed now since the first recombinant protein producing microorganisms have been developed. In the meanwhile, numerous proteins have been produced in bacteria, yeasts and filamentous fungi, as weIl as higher eukaryotic cells, and even entire plants and animals. Many recombinant proteins are on the market today, and some of them reached substantial market volumes. On the first sight one would expect the technology - including the physiology of the host strains - to be optimised in detail after a 20 year's period of development. However, several constraints have limited the incentive for optimisation, especially in the pharmaceutical industry like the urge to proceed quickly or the requirement to define the production parameters for registration early in the development phase. The additional expenses for registration of a new production strain often prohibits a change to an optimised strain. A continuous optimisation of the entire production process is not feasible for the same reasons.

The general field of fundamental and applied biotechnology becomes increasingly important for the production of biologicals for human and veterinary use, by using prokaryotic and eukaryotic microorganisms. The papers in the present book are refereed articles compiled from oral and poster presentations from the EFB Meeting on Recombinant Protein Production with Prokaryotic and Eukaryotic Cells. A Comparative View on Host Physiology, which was organized in Semmering/A from 5th to 8th October 2000. A special feature of this meeting was the comparison of different classes of host cells, mainly bacteria, yeasts, filamentous fungi, and animal cells, which made obvious that many physiological features of recombinant protein formation, like cell nutrition, stress responses, protein folding and secretion, or genetic stability, follow similar patterns in different expression systems. This comparative aspect is by far the point of most interest because such comparisons are rarely done, and if they are done, their results are most often kept secret by the companies who generated them. Audience: Presently, a comparable book does not exist because the compiling of manuscripts from all fields of biotechnology (prokaryotic as well as eukaryotic, up to animal cell biotechnology) is not done in general. This particularity makes this book very interesting for postgraduate students and professionals in the large field of biotechnology who want to get a more global view on the current state of the expression of recombinant biologicals in different host cell systems, the physiological problems associated with the use of different expression systems, potential approaches to solve such difficulties bymetabolic engineering or the use of other host cells, and the cooperation between process development and strain improvement, which is crucial for the optimisation of both the production strain and the process. This book should be in every library of an institution/organization involved in biotechnology.