Cluster headache is a disorder of unknown origin. Some studies have focused their attention on neuroendocrine derangement, others on immunity. To probe central alterations in cluster headache (CH), immune parameters were investigated in cluster headache patients in comparison to low back pain patients and healthy controls. Increases in peripheral blood monocytes found in remission cluster headache patients may be attributable to chronic central nervous system (hypothalamic?) noradrenergic dysfunction or altered beta-endorphin. Alterations in NK+, CD3+ and CD4+ levels found in cluster period cluster headache and low back pain patients are probably pain or stress-related.