Schnitzler's syndrome: a broader clinical spectrum. Schnitzler's syndrome is characterized by chronic urticaria, recurrent fever, bone pain, and lymphadenopathy in conjunction with a serum IgM M component in a concentration that is usually less than 10,000 mg/L. Complement activation and cryoprecipitation do not appear to be involved. We report two additional patients who share many of the characteristics of this entity. These patients differ from patients previously reported because of the markedly elevated IgM M-component concentration in one patient and the severity of anemia in the second patient. An increased frequency of IgG autoantibodies to interleukin-1-alpha has been reported by other investigators; it has been suggested that an antibody-mediated prolongation of the half-life of interleukin-1-alpha might account for some of the symptoms and signs of this disorder. However, neither the mediators involved in the induction of nonpruritic urticaria nor the role of the IgM M component has been established. 