It is likely that benzene expo- sures are also occurring outside of school, and this is reflected in the significantly higher levels of urinary t,t- muconic acid in the mornings before school commences. Afternoon levels were significantly higher than morning levels in Bangkok school children, indicating a signif- icant exposure during the school day (P < 0.05). The levels were comparable with levels observed in street vendors (Navasumrit et al., 2005), adults who were actu- ally exposed to higher concentrations of benzene, even