Phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopic analyses of the crystalline lens from the experimental diabetic rat were performed. Qualitative and quantitative alterations in the phosphorus-31 NMR metabolic profile were observed over the course of 3 weeks after the induction of diabetes mellitus. Most striking was the appearance of two new, as yet unidentified, metabolites. These metabolites which resonate at 6.6 and 5.8 ppm were not detected in the normal lens. Compared to the normal lens, glycerol-3-phosphate (G3P) underwent an eightfold increase in concentration and phosphorylcholine decreased to one-third its initial level. The phosphodiesters, glycerophosphorylcholine (GPC) and glycerophosphorylethanolamine (GPE), decreased to barely detectable levels. Oral treatment of the diabetic animal with an aldose reductase inhibitor resulted in the preservation of an essentially normal lens 31P NMR spectrum. Except for the changes observed in glycerol-3-phosphate, these alterations have not been previously reported and raise new questions about the metabolic consequences of diabetes mellitus and the dependence of these alterations on the action of a single enzyme, aldose reductase.