Glucose and phosphorus metabolism in mature (8-month-old) rat lenses were examined with NMR spectroscopy. Nondia-betic mature lenses contained sorbitol-3-phosphate (S3P) and fructose-3-phosphate (F3P) which were absent from young (1-to 2-month-old) normal rat lenses. The concentrations of these two phosphates can be changed through (1) diabetes induction with streptozotocin – this results in a dramatic increase in both compounds; and (2) oral dosing with a drug known to prevent sorbitol production – both metabolites disappeared. When normal mature lenses were incubated in 35.5 m M<sup>13</sup>C<sub>1</sub>-glucose, both <sup>13</sup>C<sub>1</sub>-lactate and <sup>13</sup>C<sub>3</sub>-lactate were produced. Preservation of the <sup>13</sup>C label at Q is likely through the formation of <sup>13</sup>C<sub>1</sub>-S3P and -F3P, which were then split through an aldolase-like mechanism into two 3-carbon compounds, one an unlabeled glycerol and the other <sup>13</sup>C<sub>1</sub>-α-glycerophosphate (from S3P) and <sup>13</sup>C<sub>1</sub>-dihydroxyacetone phosphate (from F3P). These reactions can contribute to the increase in α-glycero phosphate observed in both the streptozotocin-induced diabetic lenses and lenses incubated in high glucose.