Mast cells in several animal species have been found to contain heparin,1 hyaluronic acid,2 and histamine.3 In 1955, Benditt et al.4 isolated 5-hydroxytryptamine (serotonin) from the mast cells of the rat. In humans, excessive quantities of serotonin have been demonstrated only in patients with the malignant carcinoid syndrome,5 and the chromaffin cells of the gastrointestinal tract are the source of this amine.
This is the report of a case of an adult patient with urticaria pigmentosa who demonstrated some of the clinical features of the malignant carcinoid syndrome, namely, recurrent flushes and ectasias. Since serotonin has been found in mast cells of lower animal species, it was of interest to learn whether human mast cells, which are present in large numbers in the skin of patients with urticaria pigmentosa, also contain this substance. However, analysis of skin containing mast-cell infiltrates revealed no