Nuclear magnetic resonance (NMR) is a well-established tool for studying the properties of materials at the molecular level. The technique has recently been applied to the internal morphological analysis of biological material by producing a series of thin cross-sectional images derived from the distribution of mobile protons. There are grounds for believing that NMR will be more than a mere alternative to computer tomography, for it may prove possible to achieve both a useful degree of tissue characterization through analysing components of the complex NMR signal and also an approach to the measurement of blood flow in vivo.