The aim of this study was to identify a plasma biomarker of exposure to pyrethroid insecticides. A major metabolite, 3-phenoxybenzoic acid (3-PBA), can be detected in urine but urinary 3-PBA cannot be used to assess the active dose. The 3-PBA-adduct represents a much more persistent class of biomarkers than metabolites excreted into urine, having half-lives of up to several weeks or months. We developed an enzyme-linked immunosorbent assay (ELISA) for total 3-PBA including the adduct formed after alkaline hydrolysis, liquid-liquid extraction (LLE) and solid phase extraction (SPE) of the sample. The developed ELISA had an IC 50 value of 26.7 ng mL -1. The intra- and inter-assay coefficients of variation (%CV) were lower than 5% and were within the optimum condition variance (OCV) range. The LLE cleanup technique satisfactorily eliminated the matrix effect from plasma samples before SPE and ELISA analysis yielding good recoveries (85.9-99.4%) with a limit of quantitation (LOQ, 5 ng mL -1) that was 30- to 47-fold more sensitive than previous studies. Moreover, the method developed could separate more than 80% of 3-PBA from the adducted form. The method was successfully applied for the detection of the target in real samples obtained from consumers (n = 50) and farmers (n = 50). To our knowledge, this is the first ELISA method for detecting 3-PBA in the human plasma that has been applied to a field study. © 2012 The Royal Society of Chemistry.