The bcl-2 gene product inhibits apoptosis and thus its over-expression may promote development of the malignant phenotype under certain circumstances. We have introduced the bcl-2α and bcl-2β genetic elements into T cell acute lymphoblastic leukemic blasts. These transfectants were able to survive and grow in liquid culture with the establishment of cell lines while the untransfected blast cells died off. Thus transfection of the bcl-2 genes appears to give additional survival advantages to already malignant cells. Although the original leukemic blasts did not have cytoplasmic granules, the established transfectants have a morphology and surface marker profile compatible with large granular lymphoid cells.