The t(14;18) is the most frequent chromosomal aberration observed in follicular non-Hodgkin's lymphoma (NHL), and less frequently in diffuse large cell lymphoma (DLCL). The t(14;18) does not affect overall survival in follicular NHL or DLCL. It provides a unique lymphoma-specific marker that can be used to quantify residual disease during treatment, and may forward evaluation of new treatment protocols. The t(14;18) results in the deregulation of bcl-2, a proto-oncogene that protects against induction of programmed cell death (PCD). Nowadays, a whole family of bcl-2-related genes has been identified and consist of members which can either protect or promote induction of PCD. The family members form protein dimers, and the relative abundance of specific dimers regulates the cellular sensitivity to death signals (the rheostat model). Aberrant expression of different family members in several types of malignancies alter the cellular rheostat and thereby promote cellular resistance to chemotherapy.