In recent years there have been several reports on urticaria pigmentosa as just one phenomenon of a systemic mast-cell disease. Mast-cell accumulations have been demonstrated in several internal organs and tissues, giving rise to enlargements of the organs and to infiltration, rarefaction, and sclerosis of bones and other connective tissues.1-4 However, reports on symptoms arising from increased formation of mastcell products (hyaluronic acid, heparin, histamine, serotonin) have been relatively rare. The stimulated connective tissue regeneration and fibrosis, which has been noted in many cases, is depending on a release of ground-substance mucopolysaccharides of the hyaluronic acid type by the mast cells.5 Disturbances of the blood coagulation mechanism have been reported in a few cases.6 They may or may not have been related to the content of heparin-like substances in mast-cell granules.7Histamine, known to be synthesized in mast cells,8,9 may well play a role for