Biomarkers yield information as to whether an organism has been exposed to a xenobiotic (biomarkers of exposure), about the response of the organism exposed to the xenobiotic (biomarkers of effect), or about the susceptibility of the organism to xenobiotics. Biomarkers of exposure can be used to biomonitor xenobiotic exposure, even after the organism has lost physical contact with xenobiotics. In this way, adducts formed between the xenobiotic or its metabolites and an endogenous molecule are especially interesting because they remain in organisms for a longer time than the latter, circulating as free chemicals (unbound to endogenous molecules). Biomarkers of effect (response) can be used to test the consequences of exposure on the exposed organism, while biomarkers of susceptibility can be employed to predict the intensity of this effect (response). Biomarkers can yield valuable information for risk assessment when they are analyzed in an integrated strategy that considers a battery of several biomarkers of each of these three categories.