The present invention provides method and pharmaceutical composition for efficient delivery of siRNA (small interfering ribonucleic acids) into cultured mammalian cells. In addition, the present invention provides methods and compositions for knocking down the expression of a specific target gene by treating cells with the formulations comprising cationic amphiphile, a neutral colipid and a small RNA molecule. We demonstrate that our method delivers siRNA efficaciously into animal cells for the purpose of RNA interference. The area of medical science that is likely to benefit most from the present invention is RNAi therapeutics.
