Styrene is widely used in the production of various plastics, synthetic rubber and resins. Occupational exposure occurs mainly via inhalation and relatively high exposure occurs due to its use in manual application techniques. The aim of this study was to evaluate if SO-Hb adducts are a suitable biomarker for assessing occupational exposure to styrene. Seventy-five reinforced plastic workers and 77 control subjects were studied. In the selected population the main urinary styrene metabolites and the styrene oxide N-terminal valine (SO-Hb) adducts in human globin were quantified. The levels of SO-Hb adducts were significantly higher (p<0.01) in the exposed subjects (5.98pmol/g globin) when compared with controls (2.59pmol/g globin) and a significant difference was found in levels of SO-Hb adducts between non-smokers and smokers among the control group. From our data we conclude that SO-Hb adduct measurement is a sensitive and specific means of assessing exposure to styrene at the occupational and environmental level.