In the Proceedings of this Symposium, papers are presented from leading laboratories worldwide studying human and animal retroviruses and their associated leukemias and other diseases, including AIDS. The volume provides an up-to-date review of the field and indicates possible future developments for cancer research in which multidisciplinary work, ranging from molecular biology to epidemiology, plays an important role. The book contains 31 papers which are grouped into the following subject areas: lectures; clinical aspects; epidemiology; virus transmission; characterization of viruses; infected cells; AIDS.