Abstract: Gas chromatography with capillary column was applieed to the determination of residual amounts of organochlorine pesticides in human serum.The sample was diluted with formic acid and extracted with n-hexane ultrasonically.The upper organic layer was taken and sulfonated with conc.H2SO4.The sulfonated solution layer was separated and evaporated to near dryness in a vacuum dryer.The residue was taken up with 1 mL of n-hexane and used for GC analysis,with electron capture detector.Four isomers each of the pesticides DDT and BHC were separated satisfactorily and determined within 20 min.Linear relationships between values of peak area and mass concentration of the 8 isomeric compounds were obtained in the range of 0.4-10 μg·L-1,with values of detection limit (3S/N) ranged from 0.07 to 0.30 μg·L-1.Values of intraday and interday RSD′s (n=6) found were in the ranges of 2.9%-5.4% and 4.5%-8.9% respectively.Recovery was tested by standard addition method,giving values in the range of 81.5%-117.6%.