Surgical diagnosticians continue to search for a completely safe, noninvasive method of delineating in vivo anatomic structures and/ or metabolic events. To this end, a new method of forming X-ray images known as computerized axial tomography (CAT) was developed [ 55 1. Though capable of producing cross-sectional views of selected regions of virtually any part of the body, the resultant information is solely anatomical. Moreover, if structural lesions share the same electron density as surrounding tissue, even the CAT scan cannot distinguish between them. This limitation plus the acknowledged risk to pa- tients exposed to X-rays makes CAT scanning imperfect. A technique has recently evolved which promises not only to yield anatomic infor- mation at least as accurate as the CAT scan, but to image the metabolic state of the cell rather than its electron density. This tech- nique is known as nuclear magnetic reso- nance (NMR). The last decade has produced numerous studies dealing with its application to physiology and medicine. First described in 1946 by Purcell [72] at Harvard and Bloch [5] at Stanford, biologists were quick to apply this technique. Only 6 years later, the first reports of NMR application to biological ’ Recipient of an American College of Chest Physicians Research Fellowship for 1983-1984. specimens appeared [8 l] and in 1955 results from human tissue were published [70]. The recent development of methods for presenting NMR in pictorial form [59] is now providing clinical doctors with a new and powerful diagnostic tool. The purpose of this review is to examine the principles, priorities, and practice of NMR in surgical disease.