Magnetic Resonance Spectroscopy (MRS) is a method with unique capabilities-it is the only practical, non-invasive way to measure body chemistry and intracellular pH (pHi). Many of the thousands of MR imaging instruments in the world could easily be adapted to perform MRS-it adds about 10% to the capital cost. It is already widely used in clinical research, but the anticipated routine clinical methods have not yet developed. The aims of this lecture are: (i) to introduce MRS to non-specialists; (ii) to explain the biological basis of some of the spectra that are likely to be met in pattern recognition work; and (iii) to consider the classes of clinical problems amenable to this approach. (3 pages)