Cluster headache represents a primary headache disorder. The major characteristics of cluster headache are the seasonal frequency and the occurrence of symptoms during night time. A significant decrease in nocturnal melatonin levels and an advanced phase associated with a shift in cortisol acrophase has been described. The effect of lithium on nocturnal melatonin and cortisol secretion was examined in the present study. Preliminary results indicate that Lithium delaises rhythms in cluster head-ache.