Classic views of stress emphasize its links to fight or flight motivation, but very few studies have attempted to model these relationships among human beings and the relevant connections have been challenged. The present two studies (total N = 257) used a scenario-based method to examine relations among stress-related thoughts, feelings, and behaviors in response to a wide range of situational descriptions. Multilevel analyses of responses revealed strong within-person relationships, such as between estimations of stress and tendencies toward freezing, fleeing, and fighting. Individual differences in BIS motivation were predictive of stronger within-person relationships linking stress to freezing and fleeing, whereas individual differences in BAS motivation were more predictive of tendencies related to anger and fighting. The results provide novel support for biological models of stress reactivity and attest to the benefits of modeling both between- and within-person stress-related processes using a variant of the situational judgment test.