A sensitive and specific method for the determination in urine of alkoxyacetic acids, the metabolites of ethylene glycol monoalkyl ethers, was developed by combining the advantages of two previously described methods. The acids were determined gas chromatographically as their pentafluorobenzylesters. The alkylation with pentafluorobenzylbromide was performed after dissolving the dry residue of lyophilized urine in methanol. Quantitative derivatization was obtained when the urinary pH was adjusted to pH 7.0, when the reagent concentration was 5% v/v, and when the reaction mixture was heated at 90 degrees C for 3 h. Sample clean-up was performed by adding bidistilled water and the esters were extracted with methylene chloride with high yields (95%). Alkoxyacetic acid concentrations in the range of 0.1 to 200 mg/l could be determined with an average imprecision of +/- 3.5%.