Because of the current progress in molecular medicine (genomics, proteomics), a plethora of new and often human-specific targets are being identified. These targets often play a significant role in the pathogenesis of diseases, and identifying them offers the potential for early diagnosis and intervention. An early in vivo validation of specific ligands binding to these targets in humans is needed to as­ sess their potential for targeted imaging and radiotherapy. Further- VI Preface more, such validation studies may allow for a better understanding of the molecular processes underlying phannacologic activity and therefore for a more successful development of phannaceuticals in general. The purpose of the Ernst Schering Research Foundation (ESRF) Workshop 48 was to provide a forum for an open exchange on the state of the art in the early development of such radiophanna­ ceuticals. Experts from academia, industry, and regulatory authori­ ties were invited to give presentations on aspects covering the identi­ fication of targets, preclinical studies on the safety of ligands, as well as their validation in human clinical trials. It was our intention to cover both the opportunities and the challenges that scientists in this field are facing. Radiopharmaceuticals are uniquely suitable for the above-men­ tioned target validation studies.

1 Molecular Imaging: Dream or Reality?.- 2 Target Discovery and Validation.- 3 Noninvasive Imaging in Drug Discovery and Development.- 4 Internal Dose Assessment - Extrapolation from Animal Species to the Human.- 5 PET for Drug Development.- 6 Future Directions in Molecular Imaging.- 7 Regulatory Implications - The EU Perspective.- 8 Nonclinical Development of Radiopharmaceuticals: Regulatory Considerations for the United States Food and Drug Administration.- 9 The Japanese Perspective on Radiopharmaceuticals.- Previous Volumes Published in This Series.