In previous reports we have shown in SH-SY5 cells that Olomoucine and Roscovitine, two inhibitory drugs of Cyclin Dependent Kinases, caused apoptosis independent of the extrinsic pathway. In this experimental paradigm, apoptosis was refractory to the protective effects of either Bcl-2 or Bcl-XL overexpression. 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.