Recent data on the close association between chronic cold agglutinin disease (CAD) and Waldenström's macroglobulinemia (WM) have provided a new potential for therapeutic achievements. In 90% of patients with CAD, the cold agglutinins are monoclonal immunoglobulin Mkappa antibodies and clonal lymphocytes can be detected by flow cytometry of bone marrow aspirates. Bone marrow lymphoplasmacytic lymphoma is found by histology and immune histochemistry in 50% of the patients. Thus, CAD represents a spectrum of clonal lymphoproliferative disorders overlapping with WM. Conventional therapies are ineffective. Two prospective trials and 1 population-based retrospective study have shown partial response to rituximab monotherapy in 50%-55%, using strict response criteria. Median response duration was 11 months. We are currently running a prospective, uncontrolled trial of rituximab and fludarabine combination therapy. Although the preliminary results are encouraging, superiority over rituximab monotherapy remains to be proven. Patients with CAD requiring therapy should be included in clinical trials.