Oral disodium cromoglycate was found useful for the treatment of gastrointestinal manifestations of mastocytosis in 2 patients with systemic disease. The urinary excretion of histamine in these 2 patients decreased following treatment. Oral disodium cromoglycate had no effect on cutaneous symptoms, either in these 2 patients nor in 2 other patients with urticaria pigmentosa without signs of systemic mastocytosis. In the latter 2 patients the urinary excretion of histamine was unaffected. Treatment was given for 4 to 6 weeks and the dose of disodium cromoglycate was 100 mg four times daily in the 3 adult patients and 100 mg three times daily in the fourth patient, an 8-year-old boy.