Antisense agents are valuable tools to inhibit the expression of a target gene in a sequence-specific manner,and may be used for functional genomics,target validation and typesof anti-mRNAstrategies canbe distinguished. Firstly,the use of single stranded antisense-oligonucleotides; secondly,the triggering of RNA cleavage through catalytically active oligonucleotides referred to as ribozymes; and thirdly,RNA interference induced by small interfering RNA molecules.