CD40L (a member of tumor necrosis factor family) which is normally expressed on activated CD4+ T- cell, show expression on the B-cell of chronic lymphoid leukemia (B- CLL) cases. In this report, by studying with flow cytometry and florescent microscope, there were –ve correlation between CD40L % expression with HB level and increase incidence of auto-antibodies .So , CD40L may be a factor in the generation of pathologic antibodies in some patients with B-CLL. The aim of the study is to evaluate the role played by CD40L in B-CLL. We will try to answer the question: Does CD40L play a role in paracrine stimulation of B-CLL? Through this elucidation of the role of CD40L better understanding of pathphysiology of CLL would be achieved.