The actual individual uptake of polycyclic aromatic hydrocarbons (PAH) depends on a multitude of factors, and it may therefore be advantageous to supplement environmental measurements of airborne PAH compounds with biological monitoring of PAH metabolites to obtain a more reliable assessment of exposure and health risk. In the present study the applicability of determination of the urinary α-naphthol concentration as a marker for exposure to airborne naphthalene and total PAH was scrutinized. The validation is difficult since PAH compounds are widespread in the environment, and it is extremely difficult to find individuals exposed to one source of PAH compounds only. A preliminary study on five smokers employed in an office work place with no occupational PAH exposure revealed that the urinary α-naphthol concentration was closely related to the degree of smoking, i.e., heavily smoking resulted in the highest urinary α-naphthol concentrations (11.8 μmol/mol creatinine). The close correlation between smoking and elevated concentration of urinay α-naphthol was subsequently confirmed on group basis by comparison of smokers and non-smokers at four different work places, (i.e., two iron foundries with low airborne PAH exposure and two work places with unknown PAH exposure). At all work places the median values of urinary α-naphthol of smokers were higher than the median values of non-smokers, indicating that smoking may be a strong confounder when measurements of α-naphthol are used to monitor low dose of PAH exposure. In a detailed study of iron foundries the urinary α-naphthol concentration was clearly associated with the low-dose airborne total PAH exposure of the workers. This study also demonstrated the need for a careful registration of smoking habits, i.e., regardless of the level of PAH exposure. Smokers in average tended to have higher urinary α-naphthol concentrations than non-smokers. The present study has demonstrated that a newly developed liquid chromatographic method for measurement of α-naphthol in urine may be applied in biological monitoring of low dose PAH exposure.