Recent reports support the concept that the major defect in polymicrobial sepsis is an impaired immunologic response to infection. Oligodeoxynucleotides containing CpG sequence motifs (CpG-ODN) were previously shown to induce immune protection in models of chronic infection with intracellular bacteria, parasites, and viruses due to their ability to augment IFN-γ-dependent Th1 responses. Here, we demonstrate that challenging mice with CpG-ODN substantially increases the resistance against acute polymicrobial sepsis. Systemic levels of IL-12, IL-18, and IL-10 were not altered in CpG-ODN-treated mice as compared with controls. In contrast, administration of CpG-ODN resulted in a strongly enhanced accumulation of neutrophils at the primary site of infection. Neutrophils of CpG-ODN-treated mice exhibited an up-regulation of phagocytic receptors, an increased phagocytic activity, and an elevated production of reactive oxygen metabolites. These results suggest that the protective effects of CpG-ODNs in acute polymicrobial sepsis are related to an enhanced effector cell response of innate immunity. CpG-ODN may therefore represent potent agents for the treatment of sepsis-associated immunoparalysis.