A gas chromatographic procedure with mass spectrometric detection (GC-MS) was established to determine the principal amphetamines, methylenedioxymethamphetamine (MDMA), methylenedioxyethamphetamine (MDEA) and methylenedioxyamphetamine (MDA), cocaine and pharmacologically active impurities in 'ecstasy' tablets. The procedure was developed and optimised by combining the individual methods for the various drugs of abuse available in the literature into a single GC-MS run. New variants of the main drugs which may appear on the drug scene were also detected, including N-methyl-1-phenylethylamine, a member of a new series of illicit drugs. The method is rapid and has good sensitivity and reproducibility.