The mitochondria-associated adapter protein MAVS (also called IPS-1, VISA or CARDIF, designated MAVS for reasons of simplicity in our manuscript) relays signals from cytoplasmic sensors of viral RNA to the IRF3 kinase complex and the interferon-beta (IFN-beta) gene. Using siRNA-mediated knock-down in macrophages we show that IFN-beta synthesis in response to transfected, intracellular double-stranded RNA (dsRNA), a pathogen-associated molecular pattern of viruses, is decreased in absence of MAVS. By contrast, the Gram-positive bacterium Listeria monocytogenes targets the IFN-beta gene without detectable MAVS requirement. The data show that MAVS is not a central adapter protein for all cytoplasmic pathogen sensors that stimulate IFN-beta synthesis.