Gauging the progress of the next big thing in science is often difficult, as failures are often greeted with similar, if not greater, fervour as successes. No one doubts that the current flavour of the month, RNA interference (RNAi), is likely to be a scientific revolution, but in recent months several alarms have been sounded over how successfully it can be developed into safe and efficacious treatments. The latest warning call is a paper showing that mice died from liver toxicity after being injected with high doses of a certain type of RNA (Nature published online 25 May 2006 doi: 10.1038/nature04791).