Human mast cells contain large quantities of chymotryptic and tryptic proteinases. In human skin, mast cells contain both chymase and tryptase, whereas, in the mucosa of the gastrointestinal tract, mast cells contain primarily tryptase. By contrast, submucosal mast cells in the gastrointestinal tract are of the connective tissue type because they contain both chymase and tryptase. Chymase has a broad array of biological functions which include; activation of angiotensin, cleavage of basement membrane through the lamina lucida, activation of IL1 beta, and potentiation of histamine. Chymase may play a significant role in the control of a variety of biological phenomena. Urticaria pigmentosa is a disease characterized by deposition of "normal" connective tissue mast cells within the skin. The source of these mast cells is the bone marrow and mast cells appear to be deposited within other internal organs in almost all cases. Excretion of histamine and prostaglandin metabolites correlates with the deposition of mast cells in extracutaneous sites. High potency steroids under occlusion for six week results in long-lasting clearing of the cutaneous lesions with minimal side effects.