In this study, we have analyzed the consequences, on several neuroblastoma cell lines, of combined treatments with (R)-roscovitine (CYC202, Seliciclib), a CDK inhibitory drug, and nutlin-3, a p53 activating drug. Both compounds were found to synergize, causing significant levels of apoptosis in cultured cells when combined at sublethal concentrations. In SH-SY5Y cells, Bcl-XL protein overexpression protected from apoptosis induced by either nutlin-3 alone or the (R)-roscovitine plus nutlin-3 association but failed to prevent apoptosis triggered by (R)-roscovitine alone. Moreover, Western blot studies showed that (R)-roscovitine increased nutlin-3-mediated p53 stabilization. Therefore, we conclude the contribution of (R)-roscovitine to the synergism is basically the sensitization of SH-SY5Y cells to the action of nutlin-3 on p53. The relevance of this pharmacological synergism with respect to the treatment of neuroblastoma is discussed.