The canine venereal transmissible tumor (TVT) is a non differentiated round cell neoplasm frequen­tly described on mucous membranes, specially of genital organs. The allotransplantability of this tu-mor has drawn the attention of researchers interested in transplant rejection mechanisms and immune response. The cytology of this tumor is similar in some aspects to that of lymphocytes and macropha­ges, in fact it was formerly known as venereal lymphosarcoma or Sticker's sarcoma. More recently, immunophenotipic markers of histiocitic origin have been detected on TVT cells. However, these stu­dies are not conclusive due to the fact that the tumor is normally infiltrated by numerous leucocyte cells, including histiocytes from the host that are not easily distinguished from tumor cells. In this work it is proposed that TVT cells can be separated, in tumor cell suspensions, from leucocytes in a density gradient. The results show that TVT cells can not only be separated from most leucocytes in a polysu­crose and sodium diatrizoate gradient, but also that it is posible to improve the percentage of viability, possibly as damaged cells are easily destroyed by osmotic changes.