This article presents a meta-analysis of the literature on stress and immunity in humans. The primary analyses include all relevant studies irrespective of the measure or manipulation of stress. The results of these analyses show substantial evidence for a relation between stress and decreases in functional immune measures (proliferative response to mitogens and natural killer cell activity). Stress is also related to numbers and percent of circulating white blood cells, immunoglobulin levels, and antibody titers to herpesviruses. Subsequent analyses suggest that objective stressful events are related to larger immune changes than subjective self-reports of stress, that immune response varies with stressor duration, and that interpersonal events are related to different immune outcomes than nonsocial events. We discuss the way neuroendocrine mechanisms and health practices might explain immune alteration following stress, and outline issues that need to be investigated in this area.