Synthetic pyrethroid insecticides are being used with greater frequency in the United States to replace residential and some agricultural organophosphorus (OP) and carbamate insecticides. The pyrethroids are considered to be less toxic to humans than the OPs and carbamates, but like many other classes of insecticides, they are acute neurotoxicants. Barr et al. (p. 742) assessed human exposure to pyrethroid insecticides in a representative sample of the general U.S. population ? 6 years of age. 3-Phenoxybenzoic acid (3PBA), a metabolite common to many pyrethroid insecticides, was detected in > 70% of urine samples tested. Non-Hispanic blacks had significantly higher 3BPA concentrations than non-Hispanic whites and Mexican Americans, and children had significantly higher concentrations of 3PBA than adolescents and adults. Cis- and trans-(2,2-dichlorovinyl)-2,2-dimethylcyclopr ?opane-1-carboxylic acid were highly correlated with each other and with 3PBA, suggesting that urinary 3PBA was primarily derived from exposure to permethrin, cypermethrin, or their degradates. The authors conclude that pyrethroid insecticide exposure in the U.S. population is widespread and that children may have higher exposures than adolescents and adults.