The actual individual uptake of polycyclic aromatic hydrocarbons (PAH) depends on a multitude of factors, and may therefore be advantageous to supplement environmental measurements of airborne PAH compounds wit biological monitoring of PAH metabolites to obtain a more reliable assessment of exposure and health risk. In tl present study the applicability of determination of the urinary a-naphthol ~n~entration as a marker for exposure 1 airborne naphthalene and total PAH was scrutinized. The validation is difficult since PAH compounds al widespread in the environment, and it is extremely difficult to find individuals exposed to one source of PA compounds only. A preliminary study on five smokers employed in an office work place with no ~upational PA exposure revealed that the urinary ru-naphthol concentration was closely related to the degree of smoking, i.t: heavily smoking resulted in the highest urinary ar-naphthol concentrations 01.8 pmol/mol creatinine). The clor correlation between smoking and elevated concentration of urinary ~-naph~ol was sub~quently confirmed c group basis by comparison of smokers and non-smokers at four different work places, (i.e., two iron foundries wit low airborne PAH exposure and two work places with unknown PAH exposure). At all work places the media values of urinary ~-naphthol of smokers were higher than the median values of non-smokes, indicating that smokir may be a strong confounder when measurements of cr-naphthol are used to monitor low dose of PAH exposure. In detailed study of iron foundries the urinary a-naphthol concentration was clearly associated with the low-dol airborne total PAII exposure of the workers. This study also demonstrated the need for a careful registration I smoking habits, i.e., regardless of the level of PAH exposure. Smokers in average tended to have higher urinal a-naphthol concentrations than non-smokers. The present study has demonstrated that a newly developed liqui ~hromatographic method for measurement of a-naphthol in urine may be applied in biotogical monitoring of lo dose PAH exposure.