Barr et al. Interestingly, Schettgen et al. (2002) evaluated the population-based levels of 3PBA and the DCCA isomers along with other exposure factors and concluded that the German population-based concentra- tions were likely from dietary exposure. We can speculate a similar source for our U.S. population-based data; however, supplemen- tary dietary exposure data must be obtained to verify this supposition. Because residential exposures are likely periodic and vary over time, our large population sample probably minimized the contribution of these “spikes” in exposure, leaving baseline exposure con- centrations, likely from the continual dietary contributions to pyrethroid exposures. Conclusions We report the first population-based biomoni- toring data for pyrethroid metabolites for the U.S. population for the period 1999–2002. Pyrethroid pesticide exposure appears wide- spread, likely because of a shift in home pesticide use from the organophosphorus insecticides. 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