The responsiveness of the hypothalamic-pituitary-adrenocortical (HPA) system was investigated with the combined dexamethasone-corticotropin-releasing hormone (DEX-CRH) challenge test in 13 patients with "pure" panic disorder. After DEX pretreatment, this group of patients had higher CRH-induced adrenocorticotrophic hormone (ACTH) and cortisol levels than the control group, but lower than a reference group of depressed patients. The panic disorder patients were also in a middle position in the ratio of suppressors to nonsuppressors on the dexamethasone suppression test (DST) and in the ratio of normal to abnormal results on the DEX-CRH test. Our results using the combined DEX-CRH test, which is known to be much more sensitive than the original DST, support the hypothesis that HPA system functioning is altered in panic disorder patients and that this dysregulation is directly involved in the pathogenesis of the disorder.