NMR spectroscopy is an important technique for the study of biological fluids and intact cells (1-8), Compared with other analytical methods, it is nondestructive and noninvasive, and it allows delicately balanced chemical and cellular processes to be observed directly at the molecular level. 13C, 15N, 31P, and !H NMR spectroscopies have all been used to study biological fluids and/or intact cells.Because of the inherent low NMR sensitivities and low natural abundances of 13C and 15N, isotopically enriched compounds generally are used in 13C and l5N NMR studies. The advantage is a relatively simple spectrum that consists of resonances from the enriched compounds and their metabolites superimposed on much weaker background resonances. However, isotopically enriched compounds are required, and, in the case of intact cell studies, they must be incorporated into the cells. Nevertheless, 13C and 15N NMR with isotopically enriched compounds are widely used and important methods for the study of metabolic processes in intact cells, 31P, which has a natural abundance of 100% and a high inherent NMR sensitivity, is also widely used. Because there are few phosphorus-containing compounds at detectable levels, 31P NMR spectra of biological fluids and intact cells generally are relatively simple. For the same reason, however, 31P NMR can be used to study only a limited number of compounds.the analog-to-digital converter. This spectrum and all the other spectra presented In this article were measured with a Varlan VXR-500S spectrometer operated in the unlocked mode.