After birth the human brain is subject to major maturational changes, which are associated with changes in the biochemical composition of the brain and brain metabolism. Magnetic resonance (MR) spectroscopy has special capabilities in the analysis of in vivo metabolism. Volume-selective proton and phosphorus MR spectroscopy of the brain was performed on a 1.5-T magnet in 41 healthy children aged 1 month to 16 years. With advancing age, phosphorus spectra revealed a decrease in the ratios of phosphomonoesters (PMEs) to beta-adenosine triphosphate (ATP) and PMEs to phosphocreatine (PCr) and an increase in the ratios of phosphodiesters to beta-ATP, PCr to beta-ATP, and PCr to inorganic phosphate (Pi). No significant changes were observed in Pi/beta-ATP and pH. No changes occurred after the age of 3 years. Proton spectroscopy revealed an increase in the ratios of N-acetylaspartate (NAA) to choline (Ch) and NAA to creatine (Cr) and a decrease in Ch/Cr with increasing age. The most rapid changes were noted during the first 3 years of life, but changes were still observed at the age of 16 years.