Abundant evidence indicates that endogenous stress hormones such as epinephrine and corticosterone modulate memory consolidation in animals. We recently provided the first demonstration that an endogenous stress hormone (epinephrine) can enhance human memory consolidation. However, these findings also suggested that post-learning stress hormone activation does not uniformly enhance memory for all recently acquired information; rather, that it interacts with the degree of arousal at initial encoding of material in modulating memory for the material. Here we tested this hypothesis by administering cold pressor stress (CPS) or a control procedure to subjects after they viewed slides of varying emotional content, and assessing memory for the slides 1 wk later. CPS, which significantly elevated salivary cortisol levels, enhanced memory for emotionally arousing slides compared with the controls, but did not affect memory for relatively neutral slides. These findings further support the view that post-learning stress hormone-related activity interacts with arousal at initial encoding to modulate memory consolidation.Abundant evidence dating to the initial findings of McGaugh in the 1950's documents that treatments administered after learning, such as drug injections or brain stimulation, can modulate (enhance or impair) memory consolidation processes (McGaugh 2000). Abundant evidence also documents that endogenous stress hormones such as epinephrine and corticosterone also modulate consolidation in animals (McGaugh 2000;Roozendaal 2000). And recently, we provided the first demonstration that an endogenous stress hormone can modulate human memory consolidation (Cahill and Alkire 2003). This evidence forms a cornerstone of the view that enhanced memory for emotionally stressful events results from the enhancing effects of stress hormones on consolidation processes (Gold and McGaugh 1975).A widespread assumption has been that stress hormone action rather uniformly modulates memory consolidation for recently acquired information. Livingston (1967), originator of the "Now print!" metaphor about arousal's influence on memory storage, made this assumption explicit by suggesting that after an arousing/significant event "the brain 'prints' remembrance of all events immediately preceding" and that "following a . . . 'Now print!' order, everything that has been ongoing in the recent past will receive a 'Now print!' contribution in the form of a growth stimulus or a neurohormonal influence that will favor future repetitions of the same neural activities" (italics added). In contrast to this view, our recent findings with post-learning epinephrine infusions suggested that the degree of arousal associated with initial encoding of material helped determine whether postlearning epinephrine effectively modulated consolidation of the material (Cahill and Alkire 2003). Our results resembled those of Buchanan and Lovallo (2001), who found that pre-learning administration of cortisol enhanced long-term memory for relatively arousing pictur...