Molecular Biology of RNA Tumor Viruses deals with the molecular biology and biologic significance of RNA tumor viruses. Methods and procedures with broad application to diverse areas of molecular biology, including cell culture procedures, competition radioimmunoassays, molecular hybridization, oligonucleotide mapping, heteroduplex mapping, and restriction endonuclease techniques, are considered. This book is organized into 12 chapters and begins with a historical overview of tumor virology beginning with the early studies of Peyton Rous and leading up to the significant surge of activity during the later decade. The biology of endogenous retroviruses, their transmission both within and between species, and cellular regulatory factors influencing their expression are subsequently discussed. This book then addresses the nature and origin of transforming RNA viruses and gives a detailed review of knowledge concerning the genomic structure of type C viruses. Translational products encoded by the type C viral genome are examined in ensuing chapters, emphasizing the viral reverse transcriptase. Other mammalian retroviruses, including the mouse mammary tumor virus and type D isolates of primates, are also described. The book concludes by evaluating the possibility of direct etiologic involvement of either endogenous or exogenous RNA tumor viruses in human cancers. This book will be of value both to graduate students and to established investigators with specific interest in other aspects of molecular biology.