The cell line K-562, which carries bcr/abl rearrangement of type b3a2 is resistant to apoptosis induced by topoisomerase II inhibitors. K-562 cells were treated with complexes of cationic liposomes (DMRIE-DOPE and Dcchol-DOPE) and antisense oligonucleotides (AS-ODNs) directed against the b3a2 type of bcr/abl mRNA and non sense oligonucleotides (NS-ODNs), in a 3:1 lipid/DNA ratio during 72 hours, then they were incubated for a further 24 hours with idarubicin (IDA), 0.5 microgram/ml, to induce apoptosis. It was evaluated by morphology to the microscope of fluorescence. Cells treated with the complexes DMRIE-DOPE and Dcchol/DOPE with the specific AS-ODN showed a higher apoptosis percentage induced by IDA (mean +/- SD: 14.74 +/- 2.07 and 20.43 +/- 4.58, respectively) compared with controls not treated with ODNs (mean +/- SD: 8.08 +/- 0.82); (p < 0.05). These data indicate that the AS-ODNs directed against the b3a2 type of bcr-abl mRNA renders the cell line K-562 sensitive to IDA at the mentioned concentration.