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Samples from three major categories of thermal sources, namely municipal solid waste incinerators, hazardous waste incinerators and the iron and steel industry, were evaluated for common patterns of polychlorinated dibenzo-p-dioxins and dibenzofurans. The major contributors to the total of the 17 2,3,7,8-substituted congeners and to the I-TEQ were identified. It was found that Cl 8 DD was the most abundant congener in most samples. However, the highest contribution to the toxic equivalent (1-TEQ) was attributable to 2,3,4,7,8-PeCDF. More than 30% of the TEQ was a result of the presence of this congener.Hierarchical cluster analysis revealed that the emission pattern from the iron and steel industry were slightly different from those of the waste incineration. It was not possible to differentiate between emissions from municipal solid waste and hazardous waste incinerators. Linear regression identified 2,3,4,7,8-PeCDF as a potential marker analyte to predict I-TEQ concentrations of emission samples. However, whilst in theory such correlations may open new possibilities for application of screening techniques to predict the total I-TEQ of a sample of known origin by determining a single marker congener or surrogate compound, the study suggests that a screening technique based on the direct measurement of the total I-TEQ of a sample is likely to offer a more robust conceptual foundation for PCDD/F screening.