Bcl-2 is the major anti-apoptotic protein evaluated in studies aimed at understanding programmed cell death. Recent work suggests that the biological activity of Bcl-2 is modulated by proteolytic cleavage, with a 23 kDa cleaved Bcl-2 product having pro-apoptotic activity. In the current study we evaluated the effect of chemotherapy on Bcl-2 cleavage in B lineage leukemic cell lines. JM-1, SUP-B 15 and RS4 leukemic cell lines cleaved Bcl-2 to its 23 kDa form when exposed to the chemotherapeutic agents 1-beta-D-arabinofuranosyl-cytosine (Ara-C) or etoposide (VP-16). Chemotherapy induced Bcl-2 cleavage was blunted by inhibition of caspase activity. Co-culture of leukemic cells with bone marrow stromal cells during chemotherapy exposure resulted in reduced levels of 23 kDa Bcl-2 protein. These observations suggest that the bone marrow microenvironment may contribute to maintenance of residual leukemic disease during treatment by reducing generation of pro-apoptotic 23 kDa Bcl-2.