A pre-column derivatization method for the high-performance liquid chromatographic determination of taurine (1), L-glutamine (2), vitamin U (3) and L-aspartic acid (4) in pharmaceuticals has been developed. The optimum requirements for the derivatization conditions and the stability of resulting derivatives were discussed. The compounds were converted into DNT derivatives through the amino group by reaction with sodium 2,6-dinitro-4-trifluoromethylbenzenesulfonate (DNTS) in 50% sodium borate at 60 degrees C for 30 min (1), at 60 degrees C for 90 min (2), at 60 degrees C for 80 min (3) and at 80 degrees C for 90 min (4). After the reaction mixtures were acidified with dil. HCl, the derivatives were separated on a Cosmosil 3C18 (4.6 mm i.d. x 50 mm) column using 1% acetic acid-methanol (13:7) containing 2 mM sodium 1-heptanesulfonate as mobile phase with a ultra violet detector at 280 nm. The precisions of the analytical values expressed as the coefficient of variation were below 2.0%. The recoveries of 1-4 added to various commercial samples were in the range of 97.8-100.6%.