Abstract A single-column procedure, using Type UR-30 resin to develop acidic, neutral, and basic amino acids normally found in protein or peptide hydrolyzates is reported for the study, in human serum, of amino acids associated with some aminoacidopathies. Using a sodium citrate, three-buffer, step-change system, pH 3.28 (0.20 N), pH 4.30 (0.20 N), and pH 6.71 (1.0 N), the acidic and neutral amino acids are chromato-graphed in 85 min. A complete analysis including the basic amino acids requires 135 min. This resin also will perform the function of earlier resins—ie, the separation of the acidic and neutral amino acids by the simple hydrolyzate procedures and by the more complex physiologic procedures.