Oxidative stress plays critical roles in aging, cell death, and many diseases. Peroxynitrite is one of the major reactive oxygen species which mediates cell injury in a number of illnesses. It is of importance to identify the downstream events in peroxynitrite-initiated cell death cascade for preventing peroxynitrite toxicity. Ca2+-Mg2--endonucleases have been suggested as the endonucleases that execute DNA fragmentation in several apoptotic cascades. In this Study, we determined if astrocytes and neurons express the genes of Ca2+-Mg2+-endonucleases. We also tested our hypothesis that post-treatment with the Ca2+-Mg2+-endonuclease inhibitor aurintricarboxylic acid can decrease peroxynitrite-induced DNA damage and death of astrocytes. We found that both astrocytes and neurons express DNase I-like endonuclease - a major isoform of Ca2+-Mg2+-endonucleases. Treatment of astrocytes with aurintricarboxylic acid either before or after peroxynitrite exposures can profoundly decrease peroxynitrite-induced DNA damage and cell death. These results suggest that Ca2(+-)Mg(2+)-endonucleases may be a key downstream component in peroxynitrite-initiated cell death cascade in astrocytes and some other cell types, and aurintricarboxylic acid could be used to decrease peroxynitrite-induced DNA damage at delayed phases. Published by Elsevier Inc.