To investigate whether background of the BALB/c substrain affects the apoptosis of CT26 tumor after cisplatin treatment, the expression levels of Bax, Bcl-2 and Cas-3 proteins were measured in CT26 syngeneic tumors obtained from the three BALB/c substrains after 14 days exposure to cisplatin. This evidence concerns the gene BCL2 and neoplasm.