To evaluate the human exposure impact of municipal waste incinerators, dioxin and coplanar polychlorinated biphenyl (PCB) concentrations were determined in blood of 84 subjects who resided approximately 18 yr in the vicinity of two old incinerators, one located in a rural area (n=51) and the other in an industrial area (n=33). These subjects were compared with 63 controls from an unpolluted area. While no change was found in contaminant levels in residents living around the incinerator in the industrial area, subjects residing around the incinerator in the rural area possessed significantly higher serum levels of dioxins (38 vs. 24 pg TEQ/g fat) and coplanar PCBs (10 vs. 7 pg TEQ/g fat) than controls. These results were confirmed by multiple-regression analysis, showing that residence around the incinerator in the rural area (partial r2=.18) was the major contributor to dioxin accumulation followed by age (partial r2=.07). A two-way analysis of variance (ANOVA) on age-adjusted dioxin levels revealed a significant interaction between residence around incinerators and the consumption of fat from local origin, especially bovine and poultry products. Although age-adjusted dioxin levels in controls did not vary with local animal fat consumption, concentrations of dioxins in subjects living around the incinerators increased proportionally to their intake of local animal fat, with almost a doubling in subjects with a fat intake higher than 150 g fat/wk. Extrapolation from these data suggests that a significant increase of dioxin body burden is likely to occur only when dioxin emissions exceed 5 ng TEQ/Nm3, a threshold considerably above most emissions standards currently in force.