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.