In order to explore the effect of nuclear factor-kappa B (NF-kappaB) on bcl-x gene transcrtiption in drug-resistant leukemia cell line HL-60/E6, first of all, drug-resistant subline HL-60/E6 was derived by intermittently exposing HL-60 cells to 6 ng/ml epirubicin, and then bcl-x(L) mRNA levels were detected by RT-PCR after exposing HL-60/E6 cells to 5 micro mol/L AS-PS-ODN-RelA at different times. Morever, indirect immuno-fluorescence and FCM were used to demonstrate the location of NF-kappaB-RelA in HL-60/E6 cells and the efficiency of liposome-mediated ODN transfection. The results showed that RelA kept active and located at the nuclei of HL-60/E6 cells, and the efficiency of liposome-mediated ODN transfection was significantly higher than that of null ODN (P < 0.01 in 4, 6 and 12 h). Exposure of HL-60/E6 cells to 5 micro mol/L AS-PS-ODN-RelA led to a maximal 40% decline of bcl-x(L) mRNA levels. No significant change of bcl-x(L) mRNA level occurred in control group. It was concluded that NF-kappaB was involved in regulating bcl-x transcription. Suppressing NF-kappaB-RelA by antisense technology may down-regulate level of bcl-x(L) mRNA.