BACKGROUND: Aberrant expression of c-myb gene is often detected in transformed leukemic cells. Inhibition of c-myb expression by antisense oligos was shown to inhibit growth of normal as well as leukemic cells. C-myb antisense oligo for inhibition of tumor cell growth was, however, not decisive enough to be an effective anti-cancer agent. Thus, we set out to devise a systematic approach to find effective target sites for c-myb antisense oligos and to compare cellular uptake of antisense oligos complexed with different liposomes. METHODS: A computer simulation program for RNA secondary structures was employed to choose 8 potential target sites free of secondary structures along the entire c-myb mRNA sequence. Linear phosphorothioate-capped antisense oligos complementary to the selected target sites were synthesized and delivered into HL-60 and K562 cancer cell lines as liposomes complexes. RESULTS: Three of the 8 target sites were found to be relatively effective for reducing c-myb message. The three oliogs, MIJ-4, -17 and -18 were able to reduce c-myb message by more than 70% and suppressed tumor cell growth by about 70%. When three different cationic liposomes were used to facilitate the cellular uptake of antisense c-myb oligos, distinct liposome formulations were found to be comparably effective for reduction of c-myb message and inhibition of tumor cell growth. CONCLUSION: These results show that simulation of RNA secondary structure can be used to search effective target sites for antisense oligos and oligo uptake can be significantly enhanced by liposomes. However, cellular uptake of antisense oligos by liposomes needs further improvement.