Animal models are at the centre of laboratory bladder cancer (BC) research and at the same time, the bridge to the clinic. A new and very promising therapeutical approach is to silence abnormally up-regulated genes in cancer, through small interfering RNA (siRNA) molecules. Therapeutic use and success of siRNAs will largely depend on their efficient and safe in vivo delivery and on avoiding accidental off-target effects. Intravesical siRNA is a strategy which may be the best deliver option to surperficial BC like intravesical immunotherapy. Its direct action might allow a continuous intracellular exposure to effective siRNA concentrations. While the procedure of transurethral siRNA administration is promising for BC research allowing detection of new targets in BC therapy, the optimal intravesical carrier and the best target(s) to siRNA are to be determined. © Springer-Verlag 2009.273353361Overview: Bladder cancer (2008) How Many People Get Bladder Cancer?, , http://www.cancer.org/docroot/CRI/content/ CRI_2_2_1X_How_many_people_get_bladder_cancer_44.asp?sitearea, The American Cancer Society In: American Cancer Society, Atlanta. Available via ACS. 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