There is a growing demand for analytical techniques for the detection of a wide variety of residues from synthetic molecules in matrices such as soil, water, air and food. These techniques have to meet the requirements of speed and sensitivity as well as the ability to handle any matrix with minimal sample clean-up. Features of mass spectrometry combined with liquid chromatography can fulfill these requirements as is shown by this work which reports the use of ion spray ionization coupled with tandem mass spectrometry for the detection of some drug residues. In particular, the direct use of existing LC methods, originally conceived for use with some other sort of detector, is demonstrated.