Estrogen replacement has been associated with improved learning and memory in both animal and human studies. However, there is some evidence to suggest that “stress” has a detrimental effect on learning for female animals who still have naturally circulating estrogen. Interestingly, when the effects of this hormone are blocked in the body, stress no longer impairs learning. Several investigators have raised the possibility that the physiological response to stress may be exaggerated for women compared to men. Gender differences in biological systems that control the release of gonadal and stress hormones may explain why estrogen is beneficial for women under nonstressed conditions, but detrimental for them under stressed conditions. To date, no study has carefully controlled or manipulated both estrogen use and cortisol levels to further explore this issue. In this placebo-controlled, double blind, parallel-group design clinical study we will evaluate whether estrogen use exacerbates stress-related impairments in cognition for healthy postmenopausal women. Forty subjects will receive either 0.10 mg/day of transdermal beta-estradiol or a placebo skin patch for 8 weeks. In the last week of treatment, subjects will receive 90 mg/day of oral hydrocortisone or a placebo for 4 consecutive days. Scores on tests of memory, attention, and mood, as well as blood levels of estrogen and cortisol will be assessed at baseline, and at weeks 4 and 8. We predict that the estrogen+cortisol combination will have a deleterious effect on cognition and mood relative to the effects of either hormone administered alone. The results of this study are likely to provide important information regarding not only the nature of the interaction between these hormonal systems that occurs in response to stress, but also the conditions under which the beneficial effects of estrogen may be overshadowed.