IFN-g is a cytokine produced primarily by both T lymphocytes and natural killer cells and it is considered to be an attractive therapeutic molecule. In the present study, a DNA sequence encoding the mature murine IFN-g (muIFN-g) protein was cloned and expressed in the food-grade lactic acid bacterium Lactococcus lactis. The activity of recombinant muIFN-g produced by genetically engineered L. lactis was confirmed in an antiviral assay using MoV cells infected with Vesicular Stomatitis Virus. The data provide the first demonstration that a Gram-positive bacterium, L. lactis, is able to produce functional muIFN-g. This recombinant strain could lead to the development of a new, well-tolerated vector to deliver active muIFN-g at the mucosal level.