Résumé : The relaxation time T1 values and nuclear Overhauser enhancement factor for 31P signal were determined in model solutions of metabolites ATP, PCr and Pi, and AMP at two frequencies and in H2O and 2H2O solutions. The data were analyzed to resolve the contribution of different relaxation mechanisms. A knowledge of NOE is important in the light of recent applications of double resonance methods to enhance the sensitivity of in vivo 31P spectroscopy. The results show that chemical shift anisotropy is the dominant mechanism for 31P in ATP at the high field, whereas the dipolar interaction mechanism is the main feature for the 31P relaxation of PCr and Pi. The dipolar mechanism responsible for NOE originates from interactions of solvent water with 31P moiety. Implications for in vivo spectroscopy are indicated.