Since the initial description by Köhler and Milstein, MAbs have increasingly been used in the diagnosis and treatment of hematological diseases The diagnostic use of MAbs for detection and classification of hematopoietic malignancies.has recently become of increasing importance in clinical medicine by detecting various surface antigens such as clusters of differention (CDs) located on lymphoid and hematopoietic cells by immunophenotyping and immunohistochemistryRituximab (anti-CD20) was the first MAb approved for the treatment of B-cell lymphomas and also has significant activity in CLL and their use in addition to chemotherapeutic agents has improved the response rates. Recently it has also been used in the treatment of several autoimmune diseases such as ITP, AIHA, acquired haemophilia and TTP. The safety and efficacy of Other Mabs such alemtuzumab (anti-CD52), gemtuzumab ozogamicin (anti-CD33) and eculizumab are now well established for treatment of CLL, AML and PNH patients respectively.Ofatumumab anti-CD20 Mab is recently approved by the FDA for the treatment of chronic lymphocytic leukaemia.Two anti-CD20 radioconjugates, 90Y-ibritumomab tiuxetan and 131I tositumomab, have been approved for the treatment of relapsed/refractory B-cell NHL.