There is ample evidence from human and animal studies demonstrating the downward modulation of immune function concomitant with a variety of stressors. As a consequence, the possible enhancement of immune function by behavioral strategies has generated considerable interest. Researchers have used a number of diverse strategies to modulate immune function, including relaxation, hypnosis, exercise, classical conditioning, self-disclosure, exposure to a phobic stressor to enhance perceived coping self-efficacy, and cognitive-behavioral interventions, and these interventions have generally produced positive changes. Although it is not yet clear to what extent these positive immunological changes translate into any concrete improvements in relevant aspects of health, that is, alterations in the incidence, severity, or duration of infectious or malignant disease, the preliminary evidence is promising.