The use of anti-gene agents to disrupt the expression of disease-related genes could potentially be of utility in the treatment of a large number of illnesses, including most neoplasms. Traditional anti-gene agents include antisense oligonucleotides and ribozymes. Recent observations have provided evidence for another promising anti-gene technology-RNA interference (RNAi), in which the introduced double-stranded RNA (dsRNA), after a complicated series of processing steps, disrupts the expression of the targeted cellular gene. Further studies have indicated that small interfering RNAs (siRNAs) of generally 21 ∼ 23 nucleotides, which resemble the processing products of long dsRNA, can induce RNAi directly in mammalian cells. Because of their high specificity and efficiency, siRNAs might be a new class of anti-gene medicines for gene therapy applications.