This volume is based on the proceedings of a NATOjFEBSjGulbenkian Foundation sponsored Summer School held in September 1984 in Sintra Estoril, Portugal. Given the accelerated growth of knowledge in the field of cell transformation, it seemed timely to hold a summer school to discuss current developments in this area of biology as well as to evaluate emerging technology. The first article in this volume gives an evaluation of the various cellular systems to study neoplasia. Their properties as well as advantages and disadvantages are dis cussed. The second section deals with the role of oncogenes in cell transformation. Particular emphasis is given to the question of whether activated proto-one genes are cancer genes and to the func tions of oncogene products. The third part is dedicated to viruses and includes articles on papova viruses, Epstein-Barr virus, adeno virus, parvo viruses and HTLV. The fourth part deals with gene ex pression in normal and transformed cells while the concluding sec tion considers various aspects of gene regulation in eukaryotic cell s. vi PREFACE We wish to express our appreciation to Dr. Maria C. Lechner who provided valuable advice and help concerning the organization of this meeting. We are also indebted to Ms. Lisbeth Heilesen and Ms. Anne Mette Lygaard for typing the manuscripts and for their out standing administration of the meeting. J. E. Cel is February 1985 A. Graessmann CONTENTS NEOPLASTIC TRANSFORMATION SYSTEMS 1. Neoplastic Transformation Systems - Their Use In Stu- ing Carcinogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ."