Discrimination, poverty, and other aspects of the minority experience produce stress associated with health disparities. The hypothalamic-pituitary-adrenal (HPA) axis, a neuroendocrine subsystem usually monitored through assay of the hormone cortisol, is thought to play a key role in this relationship. Cortisol assay using hair specimens is a technology that promises to address important methodological problems in large-scale studies of health, well-being, and racial/ethnic status. The purpose of this study is to evaluate the potential of a hair cortisol assay-based method for studying trait-like HPA response to low to moderate levels of stress, associated with racial/ethnic discrimination and related social processes, among well-functioning young adults. The hair cortisol measure was shown to be highly reliable; it detected differences in gender and ethnic/racial identity and was correlated with a history of physical abuse and measures of experienced microaggression. The results support the promise of hair-based cortisol assay as a key methodology in health disparities research. (PsycINFO Database Record (c) 2020 APA, all rights reserved).