Dietary fish oil is believed to have a beneficial effect in various infections and in autoimmune disorders. This effect may correspond to an altered immune response. In order to discover whether the effect of dietary fish oil is different in various infections, we studied the survival of mice fed fish oil or corn oil supplemented diets and infected in the lungs with either Klebsiella pneumoniae or Streptococcus pneumoniae. 120 NMRI mice were divided into 4 groups, of which 2 groups were fed a fish oil supplemented diet and 2 a corn oil supplemented diet. After 6 weeks the mice were infected in the lungs with Klebsiella pneumoniae (fish oil groups and corn oil groups) or with Streptococcus pneumoniae serotype 3 (both groups). The survival rate was monitored. The experiment was performed twice. The survival of the mice fed fish oil enriched diet and infected with Klebsiella pneumoniae was significantly better compared with the mice fed corn oil enriched diet (p = 0.0001 and p = 0.0013). No difference was found between the mice fed corn oil enriched diet or fish oil enriched diet and infected with Streptococcus pneumoniae serotype 3 (p = 0.74 and p = 0.15). Our results indicate that dietary fish oil has a beneficial effect on survival of mice after experimental pneumoniae when infected with Klebsiella pneumoniae, but not after infection with Streptococcus pneumoniae serotype 3.