Di(2-ethylhexyl) terephthalate (DEHTP) is used as a substitute for ortho-phthalate based plasticizers like di(2-ethylhexyl) phthalate (DEHP) which are discussed and regulated due to their reproductive toxicity. We developed a fast and rugged method to quantify side chain oxidized monoesters of DEHTP in human urine, namely 5OH-MEHTP, 5oxo-MEHTP, 2cx-MMHTP and 5cx-MEPTP. Sample preparation was kept simple with enzymatic deconjugation and a two column assembly for on-line sample clean up. Metabolites were identified with authentic standards and quantified via isotope dilution LC-MS/MS. The limit of quantification was 0.2 mu g/L for 5cx-MEPTP and 5oxo-MEHTP, 0.3 mu g/L for 5OH-MEHTP and 0.4 mu g/L for 2cx-MMHTP. Accuracy (relative recovery: 95.8-111%) and precision (relative standard deviation: <7%) were highly acceptable. In a pilot biomonitoring study with 34 volunteers (aged 25-61 (median 42), 20 female and 14 male) not known to be occupationally exposed to DEHTP, we could detect 5cx-MEPTP above the limit of quantification in 94% of the samples (median: 0.9 mu g/L, maximum: 38.7 mu g/L). The other metabolites investigated were detected at a lower rate and at lower concentration levels (5oxo-MEHTP: 21%, maximum: 1.8 mu g/L; 5OH-MEHTP: 18%, maximum: 3.4 mu g/L; 2cx-MMHTP: 9%, maximum: 0.9 mu g/L). All target analytes can be regarded as promising and specific urinary biomarkers for DEHTP exposure. With this method we provide a basis for quantitatively investigating the human metabolism of DEHTP and for performing exposure and risk assessments in the general population and the working environment. (C) 2016 Elsevier B.V. All rights reserved.