Advances in epigenetics have begun to challenge the long-standing tenet that acquired traits are not inheritable. Now, Oliver Hobert and colleagues add viral defense in worms to the list of such Lamarckian examples and propose a mechanism independent of epigenetic modification in the germline (Cell, published online 22 November 2011; doi:10.1016/j.cell.2011.10.042). Viral defense is mediated by virus-derived siRNAs (viRNAs), which are produced by the host RNAi machinery and silence the viral genome. The authors test the transmission of viRNA-mediated silencing and find that the antiviral response is maintained across generations; only in RNAi-defective backgrounds does the immunity taper off after four to five generations. Long-term silencing lines were established, which showed non-Mendelian inheritance that was dependent on RNAi amplification. Epigenetic modifications were ruled out as a possible mechanism because the silencing effect remained intact in chromatin modification mutants. The authors propose diffusible viRNAs as the agent of this unusual inheritance of acquired immunity. Recently, RNAi-mediated heterochromatin formation and transcriptional silencing have been reported (Nature 479, 135–139, 2011, and Nature, published online 6 November 2011; doi:10.1038/nature10492). It will be interesting to see whether these epigenetic modifications can also be maintained across generations.