: Twenty healthy volunteers (half male) recalled and relived maximally disturbing (NEG) and maximally pleasurable (POS) emotional experiences. Forty minutes of silence, then neutral conversation, preceded and followed 40 minutes of emotion elicitation (NEG and POS randomly rotated). They were under video, cardiovascular, and immunological monitoring. Subjects reported appropriate emotions and showed significant cardiovascular activation during the NEG condition. Speech alone had an independent cardiovascular activating effect. Emotion, particularly NEG, led to further activation. NEG emotion promoted significant declines in mitogenic lymphocyte reactivity, followed by return to pre-emotion levels. A similar though less extreme decline was seen in the POS condition. There was a weak trend for elevated natural killer cell activity under the NEG condition, possibly due in part to changed trafficking patterns. Correlational findings confirmed these group effects. The decline in mitogenic reactivity during POS emotion appeared to be due to subtle degrees of tension and excitement triggered by the experimental experience regardless of the exact emotions recalled. Results suggest that immunologic processes are sensitive to influence by arousal of emotion.