Oxidized low density lipoproteins (ox-LDL) are known to behave as physiological pro-oxidants leading to the formation of intracellular reactive oxygen species. The presence of these altered lipoproteins in the human plasma has been associated with a number of morbid states, including atherosclerosis and immuno-deficiency. Common features of such pathological conditions seem to be represented by several alterations occurring in the immune system. In this work we analyze the in vitro effects of ox-LDL on both proliferative response and cytokine production of normal human peripheral blood mononuclear cells (PBMC). Our results indicate that ox-LDL significantly inhibit proliferative response and modulate cytokine network interfering both at protein secretion and mRNA synthesis level.