The electrospray ionisation-ion trap mass spectrometry (ESI-MSn) of selected hypnotic drugs, i.e. zopiclone, zolpidem, flunitrazepam and their metabolites have been investigated. Sequential product ion fragmentation experiments (MSn) have been performed in order to elucidate the degradation pathways for the [M + H](+) ions and their predominant fragment ions. These MSn experiments show certain characteristic fragmentations in that functional groups are generally cleaved from the ring systems as neutral molecules such as H2O, CO, CO2, NO2, amines and HF. When an aromatic entity is present in a drug molecule together with a nitrogen-containing saturated ring structure as with zopiclone and its N-desmethyl metabolite fragmentation initially occurs at the latter ring with the former being resistant to fragmentation. The structures of fragment ions proposed for ESI-MSn can be supported by electrospray ionisation-quadrupole time-of-flight mass spectrometry (ESI-QTOF-MS). These molecules can be identified and determined in mixtures at low ng/ml concentrations by the application of liquid chromatography (LC)-ESI-MSn which can be used for their analysis in saliva samples. This paper includes a tabulation of mass losses/signals at low m/z values for these hypnotic drugs and many others in recent publications which will be of value in the characterisation of drug metabolites of unknown structure and also natural product pharmaceuticals isolated from plants, etc. (C) 2003 Elsevier B.V. All rights reserved.