Human colon cancer SW480DDP and SW620DDP cells resistant to cisplatin exhibited stronger c-myb gene expression than the parent SW480 and SW620 cells. However, cell growth rates in the cisplatin-resistant cell lines remained similar to those of the parent cells. Antisense oligonucleotides to c-myb inhibited c-myb expression and induced increased sensitivity to cisplatin in SW480DDP and SW620DDP cells, but this did not occur with the control sense oligonucleotides. In contrast, the parent cell lines were not affected by antisense oligonucleotides to c-myb. These results indicate that the c-myb gene in human colon cancer is one of the factors related to cisplatin resistance, and support the need to develop anti-cancer therapeutics based on oncogene-targeted antisense oligonucleotide technology.