B-cell chronic lymphocytic leukaemia (B-CLL) has been described as the progressive accumulation of mature-appearing B cells in peripheral blood and bone marrow, resulting from failed apoptosis rather than from alterations in cell cycle regulation. Recent investigations suggest that high WBC and lymphocyte counts result not only from defects in apoptosis, but also from cell proliferation. In this study, we aimed to examine the process of apoptosis in B-CLL patients before and during anti-cancer therapy, to answer the question of whether this parameter would presage the response to treatment and the clinical course of the disease. We found that ex vivo spontaneous apoptosis was higher in advanced-stage (III-IV acc. Rai) than in early-stage (I-II acc. Rai) patients. In I-II Rai stage patients the percentage of ex vivo apoptotic cells after chemotherapy was higher than that of apoptotic cells prior to treatment, whereas in III-IV Rai stage patients the percentage of ex vivo apoptotic cells after chemotherapy was lower than that of apoptotic cells before the anti-cancer therapy. The results of our study, in the context of the cited literature, suggest a relationship between higher ex vivo spontaneous apoptosis before treatment in advanced-stage patients with a higher proliferation of leukaemic cells and poor outcome.