Biological magnetic resonance (NMR and EPR) is a rapidly expanding area of research with much activity in most universities and research institutions. International conferences are held biennially with an increasing number of participants. With the introduction of sophisticated and continuously im­ proving instrumentation, biological magnetic resonance is approaching the state of a common physical method in biochemical, biomedical, and bio­ logical research. The lack of monograpbs on the subject had been con­ spicuous for a long time. This gap started to close only recently. However, because of the rapid expansion and intensive research, many texts are dated by the time of their appearance. Therefore we have undertaken the editing of a series that is intended to provide the practicing chemist, biochemist, or biologist with the advances and progress in selected contemporary topics. In seeking to make the series as authoritative as possible, we have invited authors who have not only made significant contributions but who are also currently active in their fields. We hope that their expertise as well as their first hand experience as reflected in the chapters of this volume will be of benefit to the reader, inter alia, in planning his own experiments and in critically evaluating the current literature.