The utility of the derivatization reagent o-phthaJdiaJdehyde (OPA) in combination with the chiral thiol N-acetyI-L-cysteine (NAC) for the enantioselective analysis of primary amphetamines and structurally related substances has been investigated. The diastereomers obtained have been chromatographed on an achiral, reversed phase Cl8 column (125 mm x 4 mm i.d., 51~m), and detected fluorimetrically The influence of parameters affecting the chromatographic separation aswell as the derivatization reaction has been optimized, using amphetamine, norephedrine, norepinephrine and 3,4-methylenedioxyamphetamine (MDA) as model compounds. On the basis of the results obtained, possible conditions for the enantiomeric analysis of these substances are described. The selected conditions have been used successfully for the enantioselective quantitation of the compounds tested within 0.5 -10.0 I~g mL 1 concentration interval (each enantiomer), the limits of detection being 25 -50 ng mL 1. Examples of application to biological samples are also given.