Double-stranded RNA (dsRNA) has been shown to trigger sequence-specific gene silencing in a wide variety of organisms, including plant, nematode and invertebrate species. Recent intense work in the field has shown that small dsRNAs mediate sequence specific RNA degradation in the process known as RNA interference (RNAi).

This invention provides for synthetic dsRNAs (20-25 nucleotides in length) and methods that can inhibit gene-specific expression in mammalian cells. The sequence of the dsRNAs is essentially identical to a portion of the coding region of the target gene for which interference or inhibition of expression is desired. This inhibition has been shown to be superior to single-stranded antisense oligonucleotides and opens the possibility of the use of dsRNAs as reverse genetic and therapeutic tools in mammalian cells.