These examples serve to illustrate that it is now possible to investigate metabolism in intact tissues using a variety of biophysical methods. While we have concentrated on NMR methods, reflecting our own interests in using 13C as a metabolic tracer, GC-mass spectroscopy can often provide similar metabolic information and has the advantage of increased sensitivity over NMR. Combining either or both of these technologies with cleaver 'chemical biopsy' methods offers new opportunities to examine what may seem to be old metabolic questions in a much more relevant environment, the native state.