Two cases of chronic urticaria associated with macroglobulinemia are reported, and the characteristics of 13 other cases are reviewed. This entity was described by Schnitzler in 1974 and has the following characteristics: chronic nonpruritic urticaria with leukocytoclastic vasculitis, bone pains with hyperostosis, intermittent fever, and a monoclonal IgM gammopathy. Liver, lymph node, and spleen enlargement may occur. Criteria for the diagnosis of Waldenström's disease are lacking (IgM level less than 10 gm/L, no overt lymphoid proliferation in bone marrow). Other immunologic findings (complement, C₁ inhibitor, cryoglobulin, rheumatoid factor, antinucleaT antibodies) are negative or normal. Evolution is long-term with a long follow-up period. In one case a lymphoplasmocytic lymphoma developed. No adequate treatment has yet been found. Pathogenesis is unclear but seems to be caused by skin deposits of the IgM paraprotein, as attested to by the direct cutaneous immunofiuorescent findings in some cases.