Aroclor 1268, Chlorofen, and Clophen T 64 technical chlorobiphenyl formulations were examined for 75 congeners of chlorodibenzo-p-dioxin (CDD) and 135 congeners of chlorodibenzofuran (CDF) using isotope dilution technique, separation, and enrichment on silica gel impregnated with activated carbon and final high resolution gas chromatography (HRGC)/high resolution mass spectrometry (HRMS) quantification. Three the most highly chlorinated congeners of CDD were found in Aroclor 1268, Chlorofen, and Clophen T 64. In the case of CDF, the number of congeners identified was 108 with 44 coeluting in pairs and 3 in triplicate in Aroclor 1268, 16 with 4 coeluting in pairs in Chlorofen, and 88 with 46 coeluting in pairs and 3 in triplicate in Clophen T 64. The total CDD and CDF concentrations of Aroclor 1268, Chlorofen, and Clophen T 64 were 24, 160, and 8.5 ng/g and 1600, 270,000, and 4000 ng/g, respectively.No mono- to hexa-CDDs could be quantified in Aroclor 1268 (<0.03 to <1 ng/g), Chlorofen (<0.07 to <0.3 ng/g), or Clophen T 64 (<0.007 to <2 ng/g), whereas two hepta-CDDs and octa-CDD were found in all three formulations, and Chlorofen was richer in those compounds, followed by Aroclor 1268 and Clophen T 64.