To evaluate the hypothalamic-pituitary-adrenal (HPA) axis in patients with posttraumatic stress disorder (PTSD), we measured adrenocorticotropin hormone (ACTH) and cortisol responses following administration of corticotropin-releasing hormone (CRH) in 8 combat veterans with chronic PTSD. The PTSD patients had a significantly lower ACTH response to CRH compared to a control group of normal volunteers. Blunted ACTH responses occurred in patients with PTSD alone, as well as those PTSD patients who also had major depression. The cortisol response, although reduced, was not significantly different from normal. The blunted ACTH response to CRH in PTSD patients is similar to that seen in other psychiatric disorders, such as depression, panic disorder, and anorexia nervosa.