Purity >98%. B-cell lymphoma/leukemia 2 (Bcl-2) is an anti-apoptotic protein that controls cell survival by binding the BH3 domains of pro-death BAD and BAK proteins and preventing permeabilization of the mitochondrial outer membrane. This protein is tightly regulated for the homeostasis between cell growth and cell death. The gene that encodes this protein is considered an oncogene; its disruption can promote the survival of cancer cells. ABT-199 is a BH3 mimetic that selectively inhibits Bcl-2 with subnanomolar affinity (Ki < 0.010 nM), binding over 3 orders of magnitude less avidly to the related family proteins, Bcl-xL and Bcl-W (Ki s = 48 and 245 nM, respectively). ABT-199 inhibits the growth of Bcl-2-dependent cell lines and in vivo tumor xenografts. This compound has shown antileukemic activity in patients with refractory chronic lymphocytic leukemia and holds promise to address additional Bcl-2-dependent cancers.