Our previous work demonstrated that antisense oligonucleotides complementary to Bcl-2 mRNA sequences were able to reduce Bcl-2 protein expression in B-cell chronic lymphocytic leukaemia (B-CLL) cells. Furthermore, the reduction in Bcl-2 expression led to an increase in apoptotic cell death that was associated with an increase in Bax expression. In this present study antisense oligonucleotides directed towards the Bax translation initiation sequence were employed to determine whether Bcl-2 and Bax protein expression were interdependent upon one another and whether Bcl-2 antisense-induced apoptosis was mediated through a p53-dependent cell death pathway. The antisense oligonucleotide down-regulated Bax protein expression between 23.7 and 68.8% in the 20 B-CLL samples tested and significantly inhibited apoptotic cell death when compared to controls (p = 0.0001). Furthermore, these changes were independent of Bcl-2 expression suggesting that the previously observed increase in Bax expression following exposure of B-CLL cells to Bcl-2 antisense oligonucleotides was probably caused by the induction of apoptosis rather than a rheostatic response to the reduction in Bcl-2 protein expression. This notion was substantiated by the fact that p21 expression was induced in Bcl-2 antisense-treated B-CLL cells, a finding consistent with p53 activation.