Previous in vivo studies have demonstrated an apparently essential role for IL‐12 in activation of NK cells to produce IFN‐γ during P. chabaudi13, 14, 39 and P. berghei40 infections but, although IL‐18 has been causally linked to IFN‐γ production and protection in P. yoelii and P. berghei infections 41, 42, this is the first demonstration of an essential role for IL‐18 in NK‐cell activation during murine malaria. This evidence concerns the gene IFNG and infection.