The authors made an attempt at treating chronic cluster headache with ketotifen (Zaditen, Sandoz). The drug is the first known agent stabilizing the cell membrane of mast cells which may be taken orally. The treatment was administered to 15 patients giving the drug in doses of 1 mg thrice daily for 8 weeks. A very good therapeutic effect was achieved in 8 cases. Good effect was noticed in 5 cases. In 2 cases only slight improvement was obtained. Reduction in the number of headache attacks occured already in the first week of treatment and progressed gradually during 8 weeks of this treatment.