SummaryA 55-ycar old man developed recurrent episodes of severe hypotension.The diagnosis of cutaneous mastocytosis with bone marrow involvement was made by skin and bone marrow biopsy.Twenty-four hour urinary excretions of Nmethyl histamine and N-mcthylimidazoleacctic acid were significantly elevated. The patient was successfully treated with ketotifen 4 mg/day orally. The symptoms and therapeutic modalities of mastocytosis arc discussed.