Using a positron emission tomography (PET) study it was shown recently that in migraine without aura certain areas in the brain stem were activated during the headache state, but not in the headache free interval. It was suggested that this brain stem activation is inherent to the migraine attack itself and represents the so called 'migraine generator'. To test this hypothesis we performed an experimental pain study in seven healthy volunteers, using the same positioning in the PET scanner as in the migraine patients. A small amount of capsaicin was administered subcutaneously in the right forehead to evoke a burning painful sensation in the first division of the trigeminal nerve. Increases of regional cerebral blood flow (rCBF) were found bilaterally in the insula, in the anterior cingulate cortex, the cavernous sinus and the cerebellum. Using the same stereotactic space limits as in the above mentioned migraine study no brain stem activation was found in the acute pain state compared to the pain free state. The increase of activation in the region of the cavernous sinus however, suggests that this structure is more likely to be involved in trigeminal transmitted pain as such, rather than in a specific type of headache as was suggested for cluster headache.