The various tautomeric forms of the tryptophan Amadori rearrangement product, including the openchain keto form, were separated at room temperature, for the first time by HPLC, on a C-18 Ultrasphere, 5 pm, 2.0 x 150 mm reversed-phase column using 5% H3P04 (0.01 M) in CH3CN (pH 2.8) as mobile phase. The flow rate was 0.6 mL/min, and the UV detector was set a t 280 nm. At these conditions, the concentration of @-pyranose was 45.2%, a-furanose, 27.4%, @-furanose 12.5%, a-pyranose 10.lCu, and keto form 4.77". The effect of pH on the relative concentrations of each tautomer was also determined.