SYNOPSIS Regional cerebral blood flow was studied with intra‐arterial ¹³³Xenon technique in 254 areas of a hemisphere during the development of classical migraine attacks in seven patients. We describe a gradual spread of reduced cerebral blood flow starting at the posterior pole of the hemisphere and advancing in a mode quite similar to the spreading depression phenomenon of Leao. In three patients the oligemia was preceeded by focal or perifocal hyperemia. Functional activation by speech etc. was usually impaired or abolished during prodromes or accompaniments. Headache was found concommitantly with cerebral blood flow reduction and cannot be caused by reactive hyperemia in these patients. Similar findings were made in two patients studied with tomographic ¹³³Xenon technique. During induced common migraine attacks repeated cerebral blood flow studies with stationary detectors (N =3) and with tomographic technique (N =4) revealed no alterations of global or cerebral blood flow. Also tomographic determination of spontaneous common migraine attacks in four patients was normal. It is concluded that the two forms of migraine are different with respect to cerebral blood flow abnormalities and that they should be studied separately in the future. Greater interest should be directed towards the phenomenon of spreading depression as a possible model of the classical migraine attack.