PROJECT SUMMARY/ABSTRACT Hazardous drinking and posttraumatic stress disorder (PTSD) are both highly prevalent and frequently comorbid public health conditions that result in more severe clinical and functional outcomes than either individual disorder12-17. There are currently no “gold standard,” evidence-based treatments available for this comorbidity.18 Moreover, the most promising interventions for this population are marked by high rates of attrition and small treatment effect sizes19, leaving this group underserved and lacking a robust and clinically significant intervention20. Some research suggests that individual differences in distress tolerance (DT) are theoretically relevant to both hazardous drinking and PTSD21-25. DT reflects the perceived or objective ability to withstand negative affective or bodily states26. DT is relatively stable (i.e., it has trait-like qualities), but recent work indicates that it also maintains state-like qualities27, 28. State-like DT is a psychological process expressed repeatedly and continuously over time29. Past work has not integrated state-like DT in terms of PTSD and hazardous drinking comorbidity. To fill this gap and facilitate mechanistic knowledge that can inform future treatment development for this population, the proposed research will examine the following primary aims in an ecological momentary assessment (EMA) framework over a 21-day time-sampling epoch: to examine whether state-like lower DT mediates the association between PTSD symptoms at baseline and alcohol use motivation; and whether state-like DT mediates the association between PTSD symptoms at baseline and hazardous drinking. The primary hypothesis of this project is that lower state-like DT will mediate the association between baseline PTSD symptoms and alcohol outcomes listed in A.1.a. and A.2.a. In seeking to identify and understand state-like DT as a mechanism of action that may underly alcohol use and co-occurring conditions (e.g., PTSD), this proposal addresses the National Institute of Alcohol Abuse and Alcoholism (NIAAA) strategic planning goals (Objective 1a). This award will support focused training in research methods and statistical analysis that would not otherwise be possible, as well as provide the opportunity to conduct research to develop a greater understanding of state-like DT as a potential mechanism influencing PTSD- hazardous alcohol use associations.