Using 31P NMR spectroscopy, we have identified sorbitol 3-phosphate and fructose 3-phosphate in normal human erythrocytes wherein their concentrations are estimated to be 13 mumol/liter cells. Incubation of hemolysates with sorbitol, fructose and ATP suggest that both sorbitol and fructose are phosphorylated separately and directly at the 3-hydroxyl position suggesting the presence in these cells of a novel and specific kinase(s). In addition to sorbitol 3-phosphate and fructose 3-phosphate which were previously identified in the mammalian lens and sciatic nerve, erythrocytes have two extra metabolites resonating at 6.7 and 6.8 ppm in the 31P NMR spectrum. Although not identified in this study, the unusual chemical shifts of these compounds, their low pKa values and the fact that they appear as doublet in proton-coupled 31P NMR spectra, suggest that these phosphomonoesters belong to the same class of metabolites as sorbitol 3-phosphate and fructose 3-phosphate. Preliminary studies of erythrocytes from an unselected group of diabetic subjects showed an overall increase in the concentration of all four metabolites, although an overlap with normal values was noted.