This phase I/II study is designed to determine the safety and tolerability of APO866 for the treatment of refractory B-CLL not amenable to aHSCT. APO866 has shown to induce growth inhibition in cultures of a wide variety of human hematological malignant cells as well as in models with subcutaneously implanted human tumors. APO866 was considered to be safe and well-tolerated in a phase I study that treated 24 patients with advanced cancer. APO866 is administered by intravenous infusion continuously for 96 hours and is repeated every 4 weeks. In this study patients will receive only one cycle of treatment and the study endpoints will be evaluated 4 weeks after the start of infusion. Patients will be followed up for 12 weeks for safety.