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A method was developed for simultaneous determination of residues of 11 illegal natural and synthetic steroids in foods of animal origin including porcine meat, porcine liver, porcine kidney, chicken and milk. The samples were concentrated using an Oasis HLB solid phase extraction cartridge, followed by dual silica and amino-propyl cartridges for cleanup. The analytes were quantified by liquid chromatography using a phenyl column coupled to an electrospray ionization tandem mass spectrometer (LC-ESI-MS/MS) operating in negative mode for estrogens and in positive multiple reaction monitoring mode for androgens. The parameters of the mass spectrometer and the composition of mobile phase and additives were also optimized to enhance detection sensitivity. The limits of detection for target analytes ranged from 1 to 120 ng/kg in different matrices. (c) 2005 Elsevier B.V. All rights reserved.