A biomarker of human exposure to chemical agents provides a valuable parameter for assessing the extent and significance of the uptake by giving a measurement that is direct and integrated over time and exposure routes. Urinary 1-hydroxypyrene is currently tested as a biomarker for the assessment of low level environmental exposure of people to polycyclic aromatic hydrocarbons (PAH). Five examples of the application of urinary 1-hydroxypyrene methodology in the assessment of environmental exposure to PAH are presented: inhalation of tobacco smoke; inhalation of urban outdoor air; windsurfers sailing on polluted water; absorption of contaminated food; exposure in an urban area with many heavy industries. The examples illustrate that the urinary 1-hydroxypyrene test is sufficiently sensitive. Urinary 1-hydroxypyrene is an effective biomarker for the assessment of human environmental exposure to PAH.