Assessment of biomarkers that reflect objective indicators of physiological processes has become increasingly popular in psychological research on stress and aging. The current article reviews biomarkers of the neuroendocrine and immune systems, including issues related to measurement and normative age-related changes. We also discuss how exposure to stressors can provoke changes in these biomarkers and propose that stressful experiences may accelerate age-related declines in these systems. We recommend that future research examining physical health and aging incorporate dynamic and multivariate methods for assessing links between stressors and biomarkers.