The masseter muscles of six nonbruxing subjecs (five men, one woman) and six bruxing subjects (four men, two women) were assessed during chewing by nuclear magnetic resonance spectroscopy (31P-NMR). The NMR spectra were collected on a GE Sigma 1.5T whole body magnet with a double-tuned 31P/1H surface coil. Two-minute trials of rest/chewing/rest were completed three times. Averaged spectra of inorganic phosphate, phosphocreatine, and three adenosine 5' triphosphate peaks were collected in each trial. Bruxing subjects had a lower concentration of total phosphate during chewing significantly less than control subjects. The pH levels during rest and during chewing were similar in both controls and bruxers. These preliminary results suggest that bruxing subjects exhibit an altered phosphate metabolism pattern during chewing as compared to nonbruxing subjects.