Abstract31P and 3‐fluoro‐3‐deoxy‐D‐glucose (3‐FDG)19F nuclear magnetic resonance (NMR) spectroscopic investigations were performed on aged rat brainin vivo. Phosphodiester (PDE) was found to be significantly higher (p<0.05) in aged brain (18 months,n= 10) than adult controls (6 months,n= 10) suggesting accelerated phospholipid catabolism in aged brain. Inorganic phosphate (P,) levels were significantly lower (p<0.05) in aged brain (n= 5) than in normal adult controls (5= 5). The sorbitol index, a measure of aldose reductase activitiesin vivo, determined by the 3‐FDG19F NMR method, revealed that aldose reductase activities were significantly higher (p<0.05)