The anal. for polychlorodibenzodioxins and polychlorodibenzofurans on a novel multidimensional CGC-CGC-MS (capillary gas chromatog.-capillary gas chromatog.-mass spectrometry) configuration is presented. The system is based on flow controlled column switching, allowing the simultaneous isomeric sepn. of tetrachloro-, pentachloro- and hexachloro-substituted dibenzodioxins and dibenzofurans on a polar column and the anal. for heptachloro- and octachloro-substituted dibenzodioxins and dibenzofurans on an apolar column. PTV injection in the solvent vent mode allows anal. of large sample sizes approaching in this way the sensitivity of CGC-high resoln. MS.