Mice lacking surfactant protein (SP)-A (SP-A−/−) or SP-D (SP-D−/−) and wild-type mice were infected with group B streptococcus or Haemophilus influenzae by intratracheal instillation. Although decreased killing of group B streptococcus and H. influenzae was observed in SP-A−/− mice but not in SP-D−/− mice, deficiency of either SP-A or SP-D was associated with increased inflammation and inflammatory cell recruitment in the lung after infection. Deficient uptake of bacteria by alveolar macrophages was observed in both SP-A-and SP-D-deficient mice. Isolated alveolar macrophages from SP-A−/− mice generated significantly less, whereas those from SP-D−/− mice generated significantly greater superoxide and hydrogen peroxide compared with wild-type alveolar macrophages. In SP-D−/− mice, bacterial killing was associated with increased lung inflammation, increased oxidant production, and decreased macrophage phagocytosis. In contrast, in the absence of SP-A, bacterial killing was decreased and associated with increased lung inflammation, decreased oxidant production, and decreased macrophage phagocytosis. Increased oxidant production likely contributes to effective bacterial killing in the lungs of SP-D−/− mice. The collectins, SP-A and SP-D, play distinct roles during bacterial infection of the lung.