A gas chromatographic/mass spectrometric method was developed for the simultaneous determination of five synthetic pyrethroid insecticides in soil, moss and fish tissue. These pyrethroids were extracted with hexane-dichloromethane by ultrasonication and cleaned up on Florisil (soil and moss) and mixed acid/base alumina (fish) columns prior to determination by gas chromatography/negative-ion chemical ionization mass spectrometry in selected ion monitoring mode. All the pyrethroids were analyzed simultaneously in a single run on a DB5-MS 15 m capillary column. Recoveries of the pyrethroids from the three matrices at fortification levels of 10, 50 and 100 μg/kg ranged from 80 to 117%. Four determinations were made at each concentration level for each matrix. The practical determination limit of the method was in the range 0.5 to 5 μg/kg depending on the compound. This method was also applied to samples obtained from a contaminated ecosystem.