The transition to parenthood marks an important developmental stage in adult life, associated with unique challenges to the partners' conflict dialogue in the formation of the family unit. Utilizing a biobehavioral experimental design, we examined the potential positive effects of the infant on the couple's conflict discussion. One hundred forty new parents of 6-month-old infants engaged in a face-to-face marital conflict discussion, while sympathetic reactivity was recorded online from mother and father and conflict interaction was microcoded for hostility and empathy. In the experimental group, a picture of one's own infant appeared on a screen halfway into the interaction, whereas controls viewed an affectively neutral stimulus. Infant reminders decreased mothers' sympathetic arousal, whereas fathers reacted with sympathetic vigilance by preserving sympathetic arousal. For both parents, infant reminders decreased couple hostility in parent-specific ways. Results accord with life-span developmental perspectives, support evolutionary models of mothering and fathering, and suggest that infants may enhance the quality of marital dialogue during this stressful transition.