Chronic stress has been demonstrated to enhance contextual fear memory; however, the molecular mechanism is still unclear. When stressed, rats release corticosterone (CORT) to liberate energy and overcome the stressor and now more data suggest CORT plays a role in enhanced contextual fear memory. Previous studies found: 1) Chronically stressed rats have enhanced CORT response to an acute stressor; 2) A single CORT injection was sufficient to enhance memory consolidation; 3) Chronically stressed rats had enhanced contextual fear memory. This current study investigates how CORT levels change throughout the contextual fear paradigm to better understand its role associated with enhanced fear memory. We hypothesize the stress rats will have an enhanced CORT response after starting the fear paradigm compared to the control rats. To test this, male and female (n=3/group) were subjected to a four-day chronic stress paradigm. The non-stress control rats (n=3/group), remained in their cage for the duration of the paradigm. After 24 hours of the last stressor, the following blood samples were taken: 1) 30 min pre-training; 2) Immediately after training; 3) 20 min after training. The training consists of placing the rat in the operant box for 5 min with two footshocks. We expect the chronically stressed rats to have an enhanced CORT response, but the data from this study is still pending. Future studies will investigate whether CORT is necessary for the enhanced fear memory. This will be possible by blocking the synthesis of corticosterone by injecting an enzyme inhibitor, Metyrapone.