Conclusions 31P NMR now provides a totally non-invasive method of studying the metabolism of selected tissues and organs within whole animals and humans. A wide range of studies therefore becomes feasible. For example, there have been problems associated with metabolic studies of isolated organs such as the brain which are particularly sensitive to hypoxia; these problems can now be circumvented by studying the organ within the whole animal. Theories of metabolic control are based largely on studies performed in vitro, and it should now prove possible to test some of these theories directly in vivo. NMR could provide significant advances in our understanding of organ preservation and function. Finally, 31 P NMR provides a new method of studying the metabolic basis and effects of disease in humans and in animal models. The technique could also provide an objective way of assessing the effectiveness of procedures that are used in the treatment of human disease.