Our findings demonstrate the need of ex vivo chronic lymphocytic leukemia cell (CLL) treatment before the application of drugs to select the most efficient manner of the patient s therapy. The obtained results confirm the link between the outcomes of the research done under ex vivo and in vivo conditions and underline the usefulness of ex vivo studies in the individual choice of CLL treatment. Our observations provide a base for further studies on the relationship between the in vivo clinical responses of patients and ex vivo pro-apoptotic activity, and the cytotoxicity of drugs against leukemic cells. Their validation by a study comprising a much larger group of patients is needed.