Overexpression of Bcl-2 protein occurs via both t(14;18)-dependent and independent mechanisms and contributes to the survival and chemoresistance of non-Hodgkin lymphomas. HA14-1 is a nonpeptidic organic small molecule, which has been shown to inhibit the interaction of Bcl-2 with Bax, thereby interfering with the antiapoptotic function of Bcl-2. In this study, we sought to determine the in vitro efficacy of HA14-1 as a therapeutic agent for non-Hodgkin lymphomas expressing Bcl-2. Assessment of cell viability demonstrated that HA14-1 induced a dose- (IC(50) = 10 μM) and time-dependent growth inhibition of a cell line (SudHL-4) derived from a t(14;18)-positive, Bcl-2-positive, non-Hodgkin lymphoma. HA14-1 effectively induced apoptosis via a caspase 3-mediated pathway but did not affect either the p38 MAPK or p44/42 MAPK pathways. Western blot analyses of Bcl-2 family proteins and other cell cycle-associated proteins were performed to determine the molecular sequelae of HA14-1-induced apoptosis. The results show down-regulation of Mcl-1 but up-regulation of p27(kip1), Bad, Bcl-xL, and Bcl-2 proteins, without change in Bax levels during HA14-1-mediated apoptosis. Our findings further elucidate the cellular mechanisms accompanying Bcl-2 inhibition and demonstrate the potential of Bcl-2 inhibitors as therapeutic agents for the treatment of non-Hodgkin lymphomas.