G. F. FUEGER Among the many processes in Physiology few appear mo~e inviting to be studied by tracers and external imaging than the variety of the routes of migratory (blood) cells in health and disease. Much emphasis has been placed lately on the methods of labelling of the white blood cells. It is obviously quite important and necessary to refine the methods of leucocytic labelling, particularly to search for ways to label selectively a specific group of white blood cells, but there is also the need to review and keep abreast with the developing knowledge of the white blood cells themselves, especially their behaviour under pathological conditions, as seen by histology and scintigraphy, their biological properties, their immunological characteristics and the mechanisms of the control of leucocytic functions. Similarly, it appears desirable to analyze animal models of inflammation as well as to review the dosimetry and the biodistribution of labelled white blood cells in humans. This book is the result of a cooperative effort to review certain highlights of the physiology of leucocytes, labelled and unlabelled, as a corollary to the effort concerning the labelling of white blood cells. In preparing this book we aim for a better understanding and definition of the goals to be achieved by the successful labelling of the migratory cells of the body. XI CONTRIBUTORS Becker, H. Medizinische Universitaetsklinik der Uni versitaet Graz, Graz, Landeskrankenhaus, haus, Austria Bjurman, B. Department of Radiation Physics, General Hospital, Malmoe, Sweden Chiles, C.