Patients with end-stage renal disease present with an immunodeficient state paradoxically coexisting with signs of activation of immune system cells and that is accentuated rather than corrected by replacement dialysis therapy. The mechanisms of this immune system dysregulation presently under consideration are a reduced bioavailability of interleukin-2 secondary to its overconsumption by activated T cells; a downregulation of phagocyte adhesion molecules and opsonin receptors following their overexpression during dialysis with complement-activating membranes; an increased production of the cytokines interleukin-1, tumor necrosis factor-alpha, and interleukin-6 by activated monocytes and of soluble CD23 by B lymphocytes; and last, but far from least, the presence of uremic toxins. Perspectives of research are aimed at elucidating the respective role of the T helper cell subpopulations (Th-1 and Th-2) and the influence of the progression of chronic renal failure on the naturally occurring cytokine inhibitors, with the hope of better defining the rationale of strategies of immunomodulation that could be beneficial to patients with end-stage renal disease.