Free radicals are highly reactive chemicals containing an unpaired electron and are normally produced by the cellular metabolism. The oxydative stress is defined as a lack of balance between the production of free radicals and the activity of antioxydant metabolites. It induces cellular damages to lipids, proteins and membranes. Abnormal calcium metabolism can be a consequence of oxydative stress leading to increased intracellular concentrations. Calbindin D28K is a calcium binding protein which could have a neuroprotective action against various cellular insults. In this study rat cortical cell cultures were exposed during various times and at different concentrations to the couple Xanthine/Xanthine oxydase (XA/XO), which produces the superoxyde radical O2-.. Neuronal survival revealed that XA/XO is toxic for cortical cell cultures. The Calbindin D28K immunocytochemical study shows that the percentages of Calbindin positive cells are greater in surviving neurons following the XA/XO exposure compared to controls. There is a time-dependent and a dose-dependent relation between the number of surviving neurons and the percentage of Calbindin positive neurons. These results suggest that the presence of cytosolic neuronal Calbindin D28k is associated with a greater resistance to oxydative stress.