The concentrations of organic flame retardants (FRs) and dioxin-like activities in dust collected from five countries were investigated. The correlations between the concentrations of the different groups of FRs and dioxin-like activities were examined. Chlorinated paraffins (CPs, C-9 to C-31) were found in the highest concentration (median Sigma CP 700 mu g/g, range 280-4750 mu g/g), followed by organophosphate esters (median Sigma 13OPEs 56 mu g/g, range 21-110 mu g/g), halogenated flame retardants (median Sigma(17)HFRs 3.3 mu g/g, range 0.87-14 mu g/g) and polybrominated diphenyl ethers (median Sigma 17PBDEs 2.8 mu g/g, range 0.46-11 mu g/g). There were no significant differences in concentrations of the FRs among the countries but differences in PBDE and CP congener profiles were found. BDE209 predominated in dust from Australia, the UK, Sweden and China, ranging from 50 to 70% of total PBDEs. The lowest percentage of BDE209 was found in the dust from Canada, representing only 20% of total PBDEs. For CPs in dust from Sweden, the long-chain CPs (especially C-18 congeners) predominated, while for other countries, medium-chain CPs (especially C-14 congeners) predominated. The dioxin-activities of the dusts ranged from 58 to 590 pg CALUX-TEQ/g, and had a median of 200 pg CALUX-TEQ/g. There were significant positive correlations between concentrations of PBDEs and CPs with dioxin-like activities. The dioxin-like activity may be due to the presence of polychlorinated or polybrominated dioxin/furans (PBDD/DFs) or polychlorinated naphthalenes (PCNs) in the dust. The PBDD/DFs are known impurities and degradation product of the penta-BDE mixture, and PCNs are known impurities of CPs which exhibit dioxin-like activities.