BACKGROUND: The classic conception of stress involves undifferentiated negative affect and corresponding biological reactivity. The present study hypothesized a new conception that disaggregates stress into emotion-specific, contrasting patterns of biological response. METHODS: Ninety-two healthy adults engaged in stress-challenge tasks, during which cardiovascular responses, hypothalamic-pituitary-adrenocortical (HPA) axis responses (i.e., cortisol), emotional expressions (i.e., facial muscle movements), and subjective emotional experience (self-reported) were assessed. RESULTS: Pronounced individual differences emerged in specific emotional responses to the stressors. Analyses of facial expressions revealed that the more fear individuals displayed in response to the stressors, the higher their cardiovascular and cortisol responses to stress. By contrast, the more anger and disgust (indignation) individuals displayed in response to the same stressors, the lower their cortisol levels and cardiovascular responses. Individual differences in optimistic appraisals appeared to mediate these correlated patterns. CONCLUSIONS: Facial expressions of emotion signal biological responses to stress. Fear expressions signal elevated cortisol and cardiovascular reactivity; anger and disgust signal attenuated cortisol and cardiovascular reactivity, patterns that implicate individual differences in stress appraisals. Rather than conceptualizing stress as generalized negative affect, studies can be informed by this emotion-specific approach to stress responses.