ABSTRACT These two studies investigated the influence of dispositional locus of control (LOC) on subjective and physiological responses to a novel laboratory stressor task. Across two studies, 64 healthy undergraduate students, ages 18–22, completed Levenson's (LOC) scales for internal, powerful others, and chance prior to performing a video-game task. Participants rated pretask and posttask stressfulness and coping ability (i.e., measures of primary and secondary appraisal). Cardiovascular measures (heart period, HP; preejection period, PEP; respiratory sinus arrhythmia, RSA; cardiac output, CO; systolic blood pressure, SBP; diastolic blood pressure, DBP & total peripheral resistance, TPR) were recorded during 4-minute baseline and 4-minute stressor task periods. The internal LOC factor predicted pretask reports of coping ability as well as posttask reports of stressfulness. In contrast, the powerful-others LOC factor predicted cardiac changes (HP, PEP, and RSA) during the task but not cardiac output or any other vascular change measure. These results underscore the importance of using the three subscales of the Levenson LOC to assess relationships between dispositional LOC and the response to stressors because self-reported appraisals of a task are predicted by a different component of dispositional LOC than are task-related cardiovascular functions.