Surface IgD was studied together with the other Ig chains on cells from 50 patients with various immunoproliferative disorders A surface IgD was associated with a monoclonal IgM of the same light‐chain type in many cases of B‐cell malignancies: chronic lymphocytic leukemia, cold agglutinin disease, Burkitt's lymphoma presenting as acute leukemia, poorly differentiated lymphocytic lymphoma, and poorly differentiated histiocytic lymphoma supervening on macroglobulinemia Surface IgD was not detected in 3 of 20 patients with chronic lymphocytic leukemia and surface IgM and was not found on either proliferating lymphocytes or plasma cells bearing IgG, IgA, or free light chain only, nor in acute lymphocytic leukemia.