Little is known about the structures and mechanisms involved in the pathophysiology of cluster headache (CH). In this study, pupillary and cardiovascular responses to the cold pressor test (CPT) were monitored in CH patients during either an active phase of disease or a remission period in order to evaluate the oculocephalic and cardiovascular functioning of the autonomic nervous system in this form of idiopathic headache. CH patients showed a specific pattern of pupillary response on both sides during both phases of the disease. This response differed from that of controls because of an absent miosis. The pressor response to CPT was more marked in CH patients than in controls. Naloxone pretreatment caused specific and selective changes in both the pupillary and cardiovascular responses of CH patients. These data suggest a systemic sympathetic hyperactivation in response to CPT in CH patients. An oculocephalic sympathetic hypofunction is possibly associated as well as an altered opioid neuromodulation.