Gas-liquid chromatographic (GLC) methods were developed for the determination of 3-phenoxybenzyl dl-cis, trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-l-carboxylate (S–3151, permethrin or Exmin ®), its geometrical and optical isomers and its impurities. dl-Trans and dl-cis isomers were separated from each other on a 2% LAC–2R–446 column and determined by using dioctyl phthalate as an internal standard, and the overall content of S–3151 was obtained by the sum of them. Optical isomers, namely, d-cis, l-cis, d-trans and l-trans forms were hydrolysed to the corresponding acids, which were derivatized to the dia-stereoisomer esters with d-or l-2-octanol and separated from one another on a 10% silicone DC QF-1 column. The optical isomer ratios were determined by the peak area ratios. The impurities of S–3151 were identified by mass spectrometer combined with GLC on a 2% PEG–20 M column and they were determined by programmed temperature GLC.