We are now reporting the failure of Bcl-XL to prevent dell death was consistent with no effect on the kinetics of caspase activation and cytochrome c release. To further characterize this issue, we have discarded a direct effect of either Olomoucine or Roscovitine on mitochondrial permeability transition. Moreover, we have evidence that an intrinsic pathway took place in SH-SY5Y cells by demonstrating the mitochondrial translocation of a GFP-Bax construct upon transfection and treatment with CDK inhibitory drugs. Finally, we tested the effect of Olomoucine and Roscovitine on w.t., bax-/-, bak-/- and double bax-/-bak-/- MEFs. In w.t. MEFs, both drugs induced cell death by apoptosis in a dose-dependent manner. In bax-/-, bak-/- and, particularly, double bax-/-bak-/- MEFs, we observed the inhibition of apoptosis. In conclusion, Olomoucine and Roscovitine caused apoptosis through an intrinsic pathway with Bax and Bak proteins being involved.