Abstract An indirect chiral HPLC method based on the derivatization reaction with o-phthaldialdehyde and N-acetyl-L-cysteine and fluorimetric detection is applied to determine the enantiomeric purity of amino acids in pharmaceutical preparations. Three samples, vanim™ 14, tebetane, and tulgrasum were analized and their enantiomeric contents were determined. Sample preparation did not require cleanup. The validity of the method was established. The D-AA content is not always specified in the labels of these pharmaceutical preparations. Keywords: DL-Amino acidsDerivatization reactionFluorimetric detectionHPLCPharmaceutical preparations ACKNOWLEDGMENT The financial support of the Spanish DGICYT project PQU2003–00667 is gratefully acknowledged. Notes OPA, o-phthaldialdehyde; NALC, N-acetyl L-cysteine; THF, tetrahydrofuran; treaction, reaction time (min); q, flow rate (mL min1). RSD, relative standard deviation (n = 4) ; DL, detection limit. QL, quantification limit. ∗n = 4; ∗∗c = g/100 mL; ∗∗∗c = mg/capsule; (capsule amount = 0.5527 g); ∗∗∗∗c = µg/cm2; gauze (14 × 25 cm). ∗concentration of added AA mixture, ∗∗mg g−1, ∗∗∗µg cm−2.