MDM2 antagonists induce p53 stabilization and accumulation of p53 target proteins in B-CLL cells. Cells from B-CLL patients were untreated (C) or treated with 5 μM nutlin-3a (N), 0.8 μM doxorubicin (D), or 3 μM fludarabine (F) for 48 hours. Cells were lysed and analyzed by Western blot as described in “Patients, materials, and methods.” Total levels of p53, MDM2, p21, PUMA, Bax, Mcl-1, and Bcl-2 were analyzed. Viability was measured by analysis of phosphatidylserine exposure and PI uptake as described in “Patients, materials, and methods,” and has been expressed here as the percentage of nonapoptotic cells.