This book is the outcome of a meeting held in Davos, Switzerland, February 7-12, 1982 focused primarily on mononuclear phagocytes and on natural killer (NK) cells. This IX International RES Congress was attended by 489 scientists from 31 countries and there were 340 scientific presentations in oral or poster session. The essential purpose of the Congress was to bring together scientists representing various aspects of mononuclear phagocyte biology to review and examine cri~ically the effects and mechanisms of macrophage growth control as well as the participatio~ of these cells in the afferent and efferent limbs of the immune response. Additional topics included the production and distribution of mono­ nuclear phagocytes; the intrinsic and extrinsic regulation of these cells; and the origin, nature, function and regulation of NK cells. The ultimate goal of the Congress was to enhance communication between scientists in various countries and disciplines so that new research directives could be defined with which to explore basic aspects of macrophage and NK cell participation in the control of cancer and infection.