Symptoms in patients with autoreactive urticaria (ArU), a sub-form of chronic urticaria (CU), are caused by circulating histamine-releasing signals. ArU patients are readily identified by the autologous serum skin test, in which they exhibit inflammatory reactions to their serum after intracutaneous injection. CU patients who also exhibit functional autoantibodies against IgE and/or its high affinity receptor Fc(epsilon)RI are thought to suffer from autoimmune urticaria (Aiu). ArU and AiU are pathogenetically and clinically different from other sub-forms of CU.