Immunoglobulins are produced by cells of the B-lymphocyte lineage. Based on differences in the heavy chain, five immunoglobulin isotypes are known as IgA, IgG, IgM, IgD and IgE. Human IgD exists in two forms: secreted IgD (secIgD), present in small amounts in human serum, and membrane-bound IgD (mIgD), present on the surface of mature B cells. MIgD is co-expressed with membrane-bound IgM (mIgM) and plays a major role as an antigenic receptor on the surface of B-lymphocytes. IgD is expressed in normal and neoplastic mantle B cells. It is absent in most cells of normal splenic marginal zone but present in 30% to 40% of splenic marginal zone lymphomas (MZLs). Additionally, IgD may be a marker for the identification of nodular lymphocyte predominant hodgkin lymphoma. Antibody to IgD is useful for classification of B-cell derived lymphomas and plasmacytomas.