Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) from various occupational, environmental, medicinal, and dietary sources. PAH metabolites in human urine can be used as biomarkers of internal dose to assess recent exposure to PAHs. PAH metabolites that have been detected in human urine include 1-hydroxypyrene (1-OHP), 1-hydroxypyrene-O-glucuronide (1-OHP-gluc), 3-hydroxybenzo[a]pyrene, 7,8,9,10-tetrahydroxy-7,8,9, 10-tetrahydrobenzo[a]pyrene, and a number of other hydroxylated PAHs. The most widely used of these is 1-OHP-gluc, the major form of 1-OHP in human urine, by virtue of its relatively high concentration and prevalence in urine and its ease of measurement. This metabolite of pyrene can be measured as 1-OHP after deconjugation of the glucuronide with beta-glucuronidase or directly as 1-OHP-gluc without deconjugation. Elevated levels of 1-OHP or 1-OHP-gluc have been demonstrated in smokers (versus nonsmokers), in patients receiving coal tar treatment (versus pretreatment), after workshifts in road pavers (versus before shifts or versus controls), after shifts in coke oven workers (versus before shift), and in subjects ingesting charbroiled meat (versus preingestion). More importantly, this metabolite is found (at low levels) in most human urine, even in persons without apparent occupational or smoking exposure. Although measurement of these metabolites is useful in assessing recent exposure to PAHs, their value as predictive markers of biological effect or health outcomes has not been rigorously tested and at present can only be inferred by association.