The chiral derivatizing reagent N-trifluoroacetyl-L-prolyl chloride (LTPC) was used to form diastereomers of 3,4-methylenedioxymethamphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) which were resolved on an achiral gas chromatographic column using a mass spectrometer as a detector. Rats were subcutaneously dosed with 40 mg/kg of (+/-) MDMA.HCl and blood was obtained by decapitation four hours after dosing. Plasma was separated and extracted. The extract was derivatized on-column with LTPC. In addition to the two MDMA isomers, the demethylated metabolites, S(+) and R(-)-MDA were identified. In all experimental groups (male rats, food deprived male rats, female rats, post partum female rats, and mice) dosed with racemic MDMA, higher levels of the S(+) isomer of MDA relative to the R(-) MDA isomer were observed. This may be significant since it has been shown that the S(+) isomer of MDMA is the more neurotoxic isomer of the racemic drug of abuse MDMA.