This article is a review of the role of mast cells and other inflammatory cells in pathogenesis of chronic urticaria. The role of histamine in pathophysiology of chronic urticaria has been established but interaction between IgE-bound mast cells and allergen is unlikely to be the mechanism by which histamine release occurs. The authors present some factors trigger mast cell degranulation and mediator release as histamine releasing factor (HRF) generating by lymphocytes and IgE autoantibodies against mast cell and basophil IgE receptors.