The aim of this study was to evaluate the rCBF (133Xe clearance method) in migrainous patients free from attack. Fifty patients suffering from migraine without aura (group M) and 20 suffering from migraine with aura (group MA) (age range 20-50 years) were submitted to 32 channel rCBF mapping during the interictal period. The rCBF data of patients were compared with those obtained from 60 healthy control subjects (group C) and 21 patients suffering from tension-type headache (group TH). The mean (average of all channels) rCBF values were: group M=70.5 ± 13.7ml/100g/min; group MA=56.6 ± 11.4ml/100g/min; group C=62.3 ± 8.3ml/100g/min; group TH=62.1 ± 8.4ml/100g/min (F=11.93; p<0.001). As expected, patients belonging to group TH had a normal rCBF. The mean rCBF of group M was significantly higher than that of groups C and TH, while in group MA it was significantly lower than in groups C and TH. Group M showed a diffuse hyperemia, while group MA showed rCBF values significantly lower than normal in posterior regions, according to aura. Our results suggest that: (a) the rCBF pattern in migrainous patients is different from that in both controls and TH patients, even during the interictal period; (b) patients suffering from migraine with and without aura are two distinct subpopulations with opposite rCBF deviations.