Wildland firefighter's exposure to wildland fire or vegetative biomass smoke has mostly been assessed by personal monitoring to airborne pollutants. However, the use of biomarkers may accurately reflect the internal (systemic) dose received by the firefighter. In this study, we assessed occupational exposure to wildland fire smoke in 14 wildland firefighters working at prescribed burns at the Savannah River Site, South Carolina by measuring the urinary concentrations of nine hydroxylated metabolites of polycyclic aromatic hydrocarbons (OH-PAHs). Except for 1-hydroxynaphthalene, preshift median concentrations of the OH-PAHs were higher compared with the median concentrations reported among the US general population, indicating elevated exposures to PAHs among the wildland firefighters during the prescribed burn season. The postshift concentrations of OH-PAHs were 83-323% (P<0.0001) higher compared with the preshift concentrations. Higher postshift concentrations of individual OH-PAHs were observed in 49 (87.5%) to 53 (94.6%) of all the 56 pre-post sample pairs. Additionally, the cross-shift (pre- to postshift) increase in 4-hydroxy-phenanthrene urinary concentration was marginally associated (P<0.1) with work shift exposure to PM2.5 and significantly associated (P<0.05) with levoglucosan, which is a marker of wildland fire or vegetative biomass smoke. These results suggest that OH-PAHs, especially 4PHE, may be useful biomarkers of wildland fire smoke exposure.