A newly synthesized designer drug, para-methoxyethylamphetamine (PMEA) was unexpectedly detected in the postmortem specimens of fatality involving drug intoxication in 2005, Japan. For unequivocal identification, the isomeric discrimination of PMEA and its positional-isomers was performed by GC/MS with the trifluoroacetylation. In order to prove the intake of PMEA, the characteristic metabolites of PMEA were also identified by GC/MS analysis of the urine specimen with trifluoroacetylation. As a result, para-methoxyamphetamine, para-hydroxyethylamphetamine (POHEA) and para-hydroxyamphetamine were identified as the major metabolites of PMEA. For the quantitative analyses of PMEA and its three metabolites in body fluids, an automated column-switching LC/MS procedure was developed, and applied to the postmortem blood and urine specimens. In this fatal case, blood concentration of PMEA was estimated to be 12.2 microg/mL and this level seemed extremely high in comparison with lethal blood-levels of its analogues, representing acute-intoxication of the victim. Based on the quantitative results, PMEA was found to be extensively metabolized to POHEA via O-demethylation, partly followed by its conjugation.