and rural (0.09 mol/mol creatinine) residences in Denmark (Hansen etal., 2005). Levels being significantly higher in samples collected in the morning before school would suggest that exposure to PAHs was occurring outside of school, e.g. on the way to school. Despite the higher levels of exposure in Bangkok school children, afternoon urinary 1-OHP lev- els were not significantly different from morning 1-OHP levels. This is likely due, in part, to the fact that levels remain elevated each morning and additional exposure levels throughout the school day may not be enough to raise the levels significantly higher.