Regulation of malignant cell growth by the immune system has been extensively studied by cancer researchers hoping to develop immuno­ therapeutic approaches to cancer management. For years these studies revolved around the recognition and destruction of tumors by cytotox. ic immune effector cells. Recently, however, attention has focused on the leukolysins, which are the soluble cytotoxic molecules secreted by activated leukocytes, because of their anticancer activities. The purpose of this book is to give an overview of the ieukolysins, with emphasis on their ability to regulate malignant cell growth. Because this is such a new field in cancer research, there remains some confusion regarding the tenninology of. and biological activity ascribed to, the different leukolysins. Therefore, we sought to present a comprehensive review of the leukolysins currently under intensive study and to compare and contrast their biological activities in an attempt to clarify the nature of these diverse biological species. This book is intended for both immunologists conducting basic research and clinical oncologists, since it reviews not only the clinical applications of the leukolysins, but presents a current update on those leukolysins that are in early developmental stages of research and could enter into clinical trials in a few years. The introduction gives an overview of the status of research on the leukolysins. In the first section, the biological activities and biochemical characteristics of the leukolysins are presented. The lymphokines.