SYNOPSISIntraocular pressure and pulsatile ocular blood flow were recorded during and between attacks in patients suffering from cluster headache (n = 18) or chronic paroxysmal hemicrania (n=7). Similarities, as well as significant differences, were observed between the two groups of patients, pointing to fundamental differences. between the two disorders with regard to pathophysiology. Compared with healthy controls, the cluster headache patients demonstrated low pulsatile ocular blood flow values between attacks, with an increase to normal levels during pain. The chronic paroxysmal hemicrania patients, however, had normal values between attacks with a marked and significant increase to high values during attacks.