Two patients with macroglobulinemia (monoclonal IgM in the serum) and massive splenomegaly were incapacitated by progressive disease refractory to standard chemotherapy. In each case, palliative splenectomy was followed by a prompt, complete, and unexpected clinical remission with disappearance from the serum of the monoclonal IgM component. One patient remains free of disease 12 years after splenectomy. The other patient remained free of detectable macroglobulinemia for 13 years after splenectomy. A review of the literature revealed other cases of remission of macroglobulinemia attributable to splenectomy alone. Data in humans and animals suggest that the spleen may facilitate IgM secretion by normal and malignant B lymphocytes. Splenectomy should be considered a possible treatment option for patients with massive splenomegaly and macroglobulinemia who progress on chemotherapy.