Lymphoblastoid cell lines continuously pulsed with mildly oxidized low density lipoproteins, exhibited a significant increase of DNA fragmentation induced by oxidized LDL internalized by cells. DNA fragmentation was associated with an increasing number of morphologically characteristic apoptotic cells simultaneously with the increase of cytotoxicity indexes, and the activation of the poly(ADP-ribose) polymerase, a nuclear enzyme stimulated by DNA strand breaks. The potential involvement of these biochemical and morphological changes in atherogenesis is discussed.