Positive parent–child relationship quality is critical for buffering children from the effects of stress on development. It is thus vital to develop interventions that target parent–child relationship quality for families experiencing stress. We examined the moderating role of parent–child relationship quality (as measured by parental emotional availability [EA]) in the inter-generational association between parental adverse childhood experiences (ACEs) and their young children’s hair cortisol concentrations (HCCs)—a physiological marker of cumulative hypothalamic pituitary adrenal (HPA)-axis activity. Using data from 127 parent–child dyads collected by two of six ACF-funded Buffering Toxic Stress consortium sites, we tested interaction effects of parental ACEs with parental EA on young children’s (Mage=18.38, SDage=7.10) HCC. (author abstract)