Disturbed regulation of both the hypothalamic-pituitary-adrenal (HPA) axis and sympathoadrenomedullary system in posttraumatic stress disorder (PTSD) suggests that immune function, which is modulated by these systems, may also be dysregulated. Two dermatologic, in vivo measures of immune function, delayed-type hypersensitivity (DTH) and skin barrier function recovery, were examined in female subjects with PTSD and compared to measures in healthy female comparison subjects. In addition, at the time of DTH test placement, circulating numbers of lymphocyte subtypes were assessed. In separate studies, the effects of acute psychological stress on DTH and skin barrier function recovery were examined in healthy volunteer subjects. Both DTH and barrier function recovery were enhanced in women with PTSD. These findings contrast with the effects of acute stress in healthy control subjects, which was associated with suppression of DTH responses and skin barrier function recovery. There was no difference between subjects with PTSD and healthy control subjects in proportions of circulating lymphocyte subsets or in expression of the lymphocyte markers CD62, CD25, and CD45RO/CD45RA. These results suggest that cell-mediated immune function is enhanced in individuals with PTSD, a condition that imposes chronic physiologic and mental stress on sufferers. These findings contrast with suppression of DTH and skin barrier function recovery in healthy volunteers in response to acute psychological stress.