Nociceptive processing in trigeminal system is likely to undergo to significant changes in chronic pain disorders such as in primary headache. The electrophysiological testing of brainstem reflexes seems to offer a valuable adjunct to the clinical evaluation, providing direct evidence for central dysmodulation of sensory and pain neurotransmission, i.e. dishabituation pattern and reduced pain threshold. We review the contribution of trigeminofacial reflex studies in the light of those recent data supporting the view of a dysfunctional sensory processing in primary headache.