Urinary hydroxy-phenanthrene (HO-PHE) excretion in non-smokers exposed to environmental tobacco smoke (ETS) is not increased. There is no significant difference in HO-PHE excretion between smokers (S) and non-smokers (NS), though excretion seems to be slightly elevated in smokers. A diet rich in polycyclic aromatic hydrocarbons leads to a rise in urinary HO-PHE excretion as compared to a diet low in polycyclic aromatic hydrocarbons (PAH), coming close to significance. HO-PHE excretion is not correlated with the mutagenic activity in urine.