Chronic urticaria (CU), with or without angioedema, is a frequent disorder defined as the occurrence of pruritic wheals for > 6 weeks. Studies carried out in the last two decades showed that the origin of the disease is autoimmune in up to 50% of cases. Currently available treatments include antihistamines, corticosteroids and ciclosporin; recently, leukotriene receptor antagonists proved effective in a subset of patients as well. For patients with an unremitting and extremely severe disease unresponsive to standard treatments, plasmapheresis and immunosuppressive drugs have been successfully attempted. Recent findings that the autologous plasma skin test scores positive in nearly all patients and that plasmas from patients with both autoimmune and 'idiopathic' chronic urticaria are frequently characterised by signs of thrombin activation (plasma levels of prothrombin fragment F(1.2) are significantly increased) suggest that clotting cascade might be somehow involved in the pathogenesis of CU. These findings put under a new light some rather sparse studies of the effect of drugs active on the coagulation system (heparin and oral anticoagulants) in patients with CU.