IL-10 regulates the balance of an immune response between pathogen clearance and immunopathology. We show here that Mycobacterium tuberculosis (Mtb) infection in the absence of IL-10 (IL-10(-/-) mice) results in reduced bacterial loads in the lung. This reduction was preceded by an accelerated and enhanced IFN-γ response in the lung, an increased influx of CD4(+) T cells into the lung, and enhanced production of chemokines and cytokines, including CXCL10 and IL-17, in both the lung and the serum. Neutralization of IL-17 affected neither the enhanced production of CXCL10 nor the accumulation of IFN-γ-producing T cells in the lungs, but led to reduced numbers of granulocytes in the lung and reduced bacterial loads in the spleens of Mtb-infected mice. This suggests that IL-17 may contribute to dissemination of Mtb.