Leukemogenesis due to benzene exposure is of particular concern because of ongoing exposure to thousands of workers in industrial plants. Monitoring of at-risk workers is recommended and of several biomarkers, urine trans,trans - muconic acid (ttMA) determination is a helpful test. The aim of this work was to classify risk occupation for benzene exposure by urine ttMA level. Here, the author compared exposure risk ratios from 6 previous reports concerning urine ttMA determination. Of interest, the high risk occupations were found to be those which have direct contact with benzene in environmental ambient air, with petroleum fuel as the common source.