The invention relates to a new antigen termed BLA-35 specifically expressed on the surface of Hodgkin's cells, Reed-Sternberg cells and B lymphocytes, and to a new monoclonal antibody (anti-BLA-36) specific thereto. The antigen is characterized by the following properties:a molecular weight of about 36,000 D;the presence of an epitope recognized by antibody to said protein;specific expression by Hodgkin's cells and Reed-Sternberg cells in all subsets of Hodgkin's disease, and by activated and early proliferating B cells;no expression by T cells;capability of reacting with its antibody in both frozen and fixed/paraffin embedded tissues;a function associated with the growth of cells capable to express said antigen protein.