o-Phthaldialdehyde in combination with a chiral mercaptan is a powerful chiral reagent for the pre-column derivatization of many enantiomeric compounds bearing primary amino groups. The diastereoisomers formed can efficiently be resolved on conventional reversed-phase columns. Simultaneous determination of the enantiomers of various amino acids, amino alcohols and biogenic amines was achieved by gradient elution and fluorescence detection. The resolution was optimized by varying the chiral mercaptan in the reagent, Boc-L-cysteine, N-acetyl-L-cysteine and N-acetyl-D-penicillamine being used for this purpose. The resolutions were calculated. Most of the enantiomers showed good resolution with each of the three chiral mercaptans, whereas some enantiomers were only separable by one or two of them. The method was applied to the analysis of peptide hydrolysates. The composition of peptides bearing L- and D-amino acids and an amino alcohol was determined.