Despite advances in understanding the role that several physiological systems play in the occurrence of general violence, little progress has been made toward understanding biological correlates of intimate partner violence (IPV). We explored involvement of one physiological system, the hypothalamic-pituitary-adrenal (HPA) axis. Among 137 heterosexual couples expecting a first child, baseline level of HPA activity—assessed via salivary cortisol collected before a couple conflict discussion—was linked to both men's and women's violence perpetration. HPA reactivity to the conflict bout did not show an independent association with IPV. However, persisting elevation in men's, and down-regulation in women's, HPA activity during a further recovery period was linked to men's violence perpetration. Aggr. Behav. 37:492–502, 2011. © 2011 Wiley Periodicals, Inc.