Based on observations indicating histamine release in cluster headache, Ketotifen was given to 15 patients suffering from a chronic form of this disease. The drug shows a mast cell membrane stabilizing action which proved effective in the treatment of bronchial asthma. It was administered in dosage of 1 mg 3 times daily for 8 weeks. Full remission was achieved in 8 patients. A considerable improvement was noted in 2 cases, a moderate improvement in 3, and only a slight improvement in 2 cases.