Nonmarital couples' salivary cortisol responses during a likelihood of marriage discussion were assessed. Sixty-eight couple members (34 couples) in the United States independently indicated the extent to which they had experience thinking about and talking about marriage to their current partners (i.e., marriage novelty). Couples subsequently jointly graphed their chance of marriage to each other over the course of their relationship histories. Increased levels of marriage novelty predicted heightened cortisol reactivity to the joint discussion relative to cortisol responses of couple members for whom the idea of marriage was less novel. These results highlight the impact simply discussing transitions can have on individuals' physiological responses, and add to the expanding literature concerning the link between nonmarital romances and biological outcomes.