123I-IMP-SPECT brain imaging was performed in patients with classic migraine (n = 5) and migraine accompagnée (n = 18) during the headache-free interval. A regional reduction of tracer uptake into brain was observed in all patients with migraine accompagnée, while in patients with classic migraine only one case showed an area of decreased activity. The most marked alteration was found in a patient with persisting neurological symptoms ("complicated migraine"). In most cases the areas of decreased tracer uptake corresponded to headache localization as well as to topography of neurologic symptoms during migraine attacks. It may be concluded that migraine attacks occur in connection with exacerbations of preexisting changes of cerebral autoregulation due to endogenous or exogenous factors.