ABT 199, a BH3 mimetic, is a targeted agent which promotes apoptosis by inhibiting BCL-2. Preliminary results on the activity of this agent report overall response rate of 84% in 56 patients with CLL. Treatment with ABT 199 was accompanied by a significant decrease in bone marrow infiltrate and lymphocyte count reduction. High response rates (89%) were observed in 27 patients with fludarabine refractory disease.