With use of a modified surface coil technique, the authors recorded phosphorus-31 magnetic resonance (MR) spectra of the brains of 40 neonates and infants (48 examinations) ranging from 33 weeks postconceptional age to 6 years of age. Signals of phosphorus metabolites were collected in the frontotemporal region of the brain, and various P-31 MR spectral variables were compared at different times during postnatal life. The ratio of the phosphomonoester signal to the phosphodiester signal, which is related to phospholipid synthesis, decreases within the first 6 months of life; during the same time period, the ratio of the phosphocreatine (PCr) signal to the beta-adenosine triphosphate (ATP) signal increases. In addition, a difference was observed between the areas under the alpha- and beta-ATP peaks. This difference increases with age and correlates with the PCr/beta-ATP signal ratio. The variation of the alpha-ATP peak with age might be explained by overlap of the signals of nicotinamide adenine dinucleotide (NAD) and alpha-ATP.