Preparing manuscripts with figures and tables for camera repro duction was a formidable task. Care has been taken for consistency and typographic accuracy. However, I make no claim that no errors exist in this volume. ,I hope, however, that the reader will under stand and ignore any error and find this compendious volume useful for numerous biologic studies, physiologic explorations and clinical app lications of radiolabeled cellular blood elements in years to come. M. L. Thakur Editor, and the ASI Director ACKNOWLEDGEMENTS Dr. Max Hardeman of the University of Amsterdam and Dr. Michael Ezekowitz of Yale University served as the codirectors of the Advanced Study Institute (ASI). Dr. Hardeman spent countless hours and contri buted to the scientific program, took care of mailings in Europe, organized transportation in Italy, and communicated with the hotel management on numerous occasions. I cannot thank him enough! Dr. Ezekowitz collected some manuscripts and corrected a few. I am grateful to him. I take this opportunity once again to thank all the guest fac ulty, who, despite their busy schedules and time constraints, accepted my invitation and made valuable contributions to the ASI. I am also grateful to all participants, who were so friendly and were primary resources for many lively discussions. They made the ASI profession ally beneficial and socially enjoyable.