The classical stimulants amphetamine, methamphetamine, ethylamphetamine and the amphetamine-derived designer drugs MDA, MDMA ('ecstasy'), MDEA, BDB and MBDB have been widely abused for a relatively long time. In recent years, a number of newer designer drugs have entered the illicit drug market. 4-Methylthioamphetamine (MTA), p-methoxyamphetamine (PMA) and p-methoxymethamphetamine (PMMA) are also derived from amphetamine. Other designer drugs are derived from piperazine, such as benzylpiperazine (BZP), methylenedioxybenzylpiperazine (MDBP), trifluoromethylphenylpiperazine (TFMPP), m-chlorophenylpiperazine (mCPP) and p-methoxyphenylpiperazine (MeOPP). A number of severe or even fatal intoxications involving these newer substances, especially PMA, have been reported. This paper describes a method for screening for and simultaneous quantification of the above-mentioned compounds and the metabolites p-hydroxyamphetamine and p-hydroxymethamphetamine (pholedrine) in human blood plasma. The analytes were analyzed by gas chromatography/mass spectrometry in the selected-ion monitoring mode after mixed-mode solid-phase extraction (HCX) and derivatization with heptafluorobutyric anhydride. The method was fully validated according to international guidelines. It was linear from 5 to 1000 micro g l(-1) for all analytes. Data for accuracy and precision were within required limits with the exception of those for MDBP. The limit of quantification was 5 micro g l(-1) for all analytes. The applicability of the assay was proven by analysis of authentic plasma samples and of a certified reference sample. This procedure should also be suitable for confirmation of immunoassay results positive for amphetamines and/or designer drugs of the ecstasy type.