This paper describes advancements in the gas chromatography-electron capture detector (GC/ECD) determination of octachlorodibenzodioxin (OCDD) and octachlorodibenzofuran (OCDF). OCDD and OCDF (OCDD/F) serve as markers or surrogates for the more toxic polychlorinated dibenzodioxins and dibenzofurans (PCDD/Fs). The current procedure allows baseline separation of OCDD/F on DB-17 capillary narrow-bore or megabore columns. OCDD/F are relatively involatile, but can be successfully injected using capillary on-column or packed column inlets (for megabore columns), and the latter can be automated. Soil method detection limits (MDL) have been reduced by a factor of ten to 0.4 to 0.8 ng/g for OCDD and OCDF, respectively, sensitivity comparable to GC/MS procedures. An optional Florisil® cartridge cleanup isolates OCDD/F from chlorinated pesticides, polychlorinated biphenyls and other coextracted environmental chemicals. Instrument detection limits for OCDD and OCDF in eggs are in the 0.5 – 1.0 ng/g lipid range after defatting samples by gel permeation chromatography (GPC).