One short sequence of RNA protected mice from deadly brain inflammation caused by West Nile virus and Japanese encephalitis virus, report Priti Kumar, Manjunath Swamy, and Premlata Shankar. The findings, which appear online and in the April 2006 PLoS Medicine, underscore the therapeutic potential of the fast-moving field of RNA interference. It has only been four years since scientists first showed that RNA interference, which protects plants, flies, and worms from viral infections, also works in mammalian cells. Now, at least two experimental siRNA therapies already have advanced to phase I safety trials in people. Short interfering RNA (siRNA) silences genes most commonly by triggering the destruction of RNA before proteins can be made.