A mouse model of polymicrobial sepsis induced by cecal content injection (CCI) was developed with the aim of gaining a better understanding of the mechanism of sepsis. This model has a similar survival pattern to the conventional model with the added benefits of ability to vary the severity of sepsis and greater consistency. Administration of 1-methyl-D-tryptophan (1-MT) to inhibit indoleamine 2,3-dioxygenase (IDO) in mice with CCI-induced sepsis increased the survival rate and tended to up-regulate IL-10/IL-12 serum concentrations. The effectiveness of 1-MT was confirmed by increases in IL-10 over IL-12 in bone marrow-derived dendritic cells (BMDCs) treated with LPS and 1-MT and a superior survival rate 24 hr after injection of these double treated BMDCs in the CCI-induced sepsis model. Therefore, CCI is both a useful and reliable technique for investigating polymicrobial sepsis. The present findings using this newly developed model suggest that inhibition of IDO alleviates the severity of polymicrobial sepsis and modulates the immune response even in cases of severe systemic septic inflammation.