In this study the 24-h pattern of blood pressure (BP), heart rate (HR), plasma catecholamine (CA), beta-endorphin (beta-EP), beta-lipotropin (beta-LPH) and RIII threshold was investigated in a patient suffering from chronic paroxysmal hemicrania (CPH). The investigation was carried out before and during indomethacin therapy in order to assess the presence or otherwise of a disordered biorhythmic organization resembling that documented in cluster headache (CH). A severe alteration in the majority of the rhythms explored was found not only during the drug-free phase, but also in the indomethacin phase of the investigation. These data are similar to those obtained in CH studies and point to the possibility of a common pathophysiological mechanism.