The bcl-2 oncogene is expressed in lymphoid and myeloid cells as well as in neurons and several types of epithelial cells and inhibits programmed cell death (apoptosis). Deregulation by the t(14;18) translocation in lymphoid malignancies induces inappropriate cell survival and serves as one of the steps toward a fully malignant behavior. Using pre- and posternbedding immunoelectron microscopy in normal and neoplastic lymphocytes, we demonstrate bcl-2 immunoreactivity to the mitochondrial outer circumference and the nuclear envelope and to a lesser degree to the cell membrane. Mitochondrial staining was patchy, reminiscent of mitochondrial contact zones. Additionally, there was a suggestion of association with nuclear pores. In these regions, transmembrane transport is mediated. This may suggest that bcl-2 exerts its function in this process.