B lymphocytes are subject to selection within germinal centers following somatic hyper-mutation on immunoglobulin variable region genes based on their ability to bind antigen with high affinity. Non-selected cells die by apoptosis. Tumors with features of germinal center B cells include follicular center cell lymphoma and Burkitt's lymphoma. We have used the latter extensively as a neoplastic model of germinal center cells and have compared directly the behaviour of cell lines derived from biopsy material with that of the normal counterparts. Here we describe some of our findings in the two systems with regard to signals regulating survival and apoptosis.