Progress in biological research has, in recent years, been characterised by its acceptance of, and dependence on, an ever increasing number of physical methods. The rapid expansion and the wideranging nature of biological applications of magnetic resonance methods represent important aspects of this development. A discussion of such applica.tions of magnetic resonance forms the subject of the present volume, which is the third in a continuing series that aims t o provide chemists, biochemists and biologists, working in this inter-disciplinary area with the information necessary for evaluating current literature and for planning future experiments.The volume contains five essays on new applications of multiple irradiation methods in magnetic resonance studies of biological molecules, contributed by authors who are leading research workers in their respective fields. R. M. Keller and K. Wuthrich (Zurich) survey multiple irradiation proton nuclear magnetic resonance measurements on haemoproteins, which provide, inter alia, information on the pathways by which electrons are transferred to and from haem-iron during biological oxidationreduction reactions. Such measurements can, also, complement comparative studies of related proteins by providing data on structural features that are not easily observed by other techniques.N. D. Chasteen (Durham, NH, USA) reports on the growing interest in employing the oxycation VO2+ as an electron spin resonance (ESR) spin probe for investigating proteins, nucleic acids, liquid crystals and biogeochemical systems.'The chemical and spectroscopic properties of the V02+ ion make it particularly useful as a n ESR probe. ESR methods for examining calcium-and proton-induced phase separations in phosphatidylserinephosphatidylcholine mixed membranes are described by S. Ohnishi and S. Tokutomi (Kyoto). After providing experimental details for preparing spin-labelled membranes, they report the results of phase separations on such membranes and discuss competition between calcium and hydrogen ions.

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