We obtained P-31 magnetic resonance spectra from the brains in vivo of 101 males (range 6-72 years). In addition, cognitive test data were obtained from 42 boys (6-13 years) and from 26 adult males (22-56 years) of this test group. Significant correlations were observed in both adults and children between various inorganic phosphate (Pi)-containing P-31 peak ratios [e.g. Pi/adenosine triphosphate (ATP)] and (predominantly verbal) cognitive tasks. No change in the Pi/ATP ratio was observed across the age range studied. Brain pH was shown to decrease significantly with age in a relationship best described by a decaying exponential. This indicated that brain pH does not stabilize at adult values until at least the late teens. We explored the possibility of a relationship between brain pH and neuronal density. In particular, we noted that our previous observation of a relationship between pH and IQ in children was not readily detected in the adult populations, whereas phosphorus metabolite ratios (in particular, those containing Pi) were found to correlate with (predominantly verbal) cognitive task performance in both adults and children. We assessed how these observations may be interpreted in the context of a metabolic vs. histological debate. Copyright (C) 2003 S. Karger AG, Basel.