We have developed and validated a new, reliable and very sensitive method for the determination of the urinary metabolites of the most common pyrethroids in one analytical run. After acidic hydrolysis for the cleavage of conjugates, the analytes cis-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (cis-Cl(2)CA), trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (trans-Cl(2)CA), cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (Br(2)CA), 4-fluoro-3-phenoxybenzoic acid (F-PBA) and 3-phenoxybenzoic acid (3-PBA) were extracted from the matrix with a liquid-liquid extraction procedure using n-hexane under acidic conditions. For further clean-up, NaOH was added to the organic phase and the carboxylic acids were re-extracted into the aqueous phase. After acidification and extraction into n-hexane again, the metabolites were then derivatised to volatile esters using N-tert.-butyldimethylsilyl-N-methyltrifluoroacetamid (MTBSTFA). Separation and detection were carried out using capillary gas chromatography with mass-selective detection (GC-MS). 2-Phenoxybenzoic acid (2-PBA) served as internal standard for the quantification of the pyrethroid metabolites. The limit of detection for all analytes was 0.05 microg/l urine. The RSD of the within-series imprecision was between 2.0 and 5.4% at a spiked concentration of 0.4 microg/l and the relative recovery was between 79.3 and 93.4%, depending on the analyte. This method was used for the analysis of urine samples of 46 persons from the general population without known exposure to pyrethroids. The metabolites cis-Cl(2)CA, trans-Cl(2)CA and 3-PBA could be found in 52, 72 and 70% of all samples with median values of 0.06, 0.11 and 0.16 microg/l, respectively. Br(2)CA and F-PBA could also be detected in 13 and 4% of the urine samples.