We used synthetic RNA transcripts to prove the cleavage capability of ribozymes targeted against bcl-2-related RNAs. No cleavage occurred when control oligonucliotides were used. To assess the functional role of the specific ribozymes in chronic myelogenous leukemia (CML) cell lines we cultured K562, BV173, and Daudi cells for 48 h after lipofection with 10 microM oligonucleotide. An increase in apoptotic cells, dependent on ribozyme specificity, was shown in BV173 cells. This finding was underlined by the typical morphological changes, but there is no correlation with regard to the level of bcl-2 protein expressed. Though bcl-2 appears to interfere with cell death in myeloid cells, bcl-2-targeted ribozymes do not induce programmed cell death (PCD) by reducing bcl-2 protein levels, but rather by a presently unknown mechanism.