Lymphocytopenia is a poor prognostic marker in initial staging of non- Hodgkin lymphomas (below 1.0 x 10(9)/l) and Hodgkin lymphoma (below 0.6 x 10(9)/l) and in relapsed diffuse large B cell lymphoma. Early lymphocyte recovery > or =0.5 x 10(9)/l after autologous and allogeneic stem cell transplantation is a significant predictor of tumor control and survival in lymphomas. Natural killer cells are involved in tumor cell killing and are the only subset of lymphocytes associated with disease outcome in initial staging and after autologous stem cell transplantation in lymphomas. The antitumor effect of various NK cell subsets should be defined.