Progress in antisense technology has been rapid, and the traditional antisense inhibition of gene expression has now been viewed at a genomic scale. This global view has led to a deeper understanding of the mechanism of action, the elimination of non-specific and undesirable side effects and, ultimately, greater efficacy and reduced toxicity for nucleic acid medicines. Several antisense oligonucleotides are in clinical trials; these are well tolerated and have therapeutic potential. Antisense oligonucleotides are promising molecular medicines with potential to treat human cancer in the foreseeable future.