Matrix metalloproteinases (MMPs) have been identified as mediators of brain injury in multiple sclerosis (MS) and it has recently been reported that treatment of MS patients with interferon-beta (IFN-beta) reduces MMP-9 serum levels and in vitro release from monocytes. We investigated whether IFN-beta is able to modulate the expression of MMPs in glial cell cultures. Rat microglial and astrocyte cultures were treated with different doses of IFN-beta, then activated by exposure to LPS. In another set of experiments cells were simultaneously activated with LPS and treated with IFN-beta. Culture supernatants collected from astrocytes and microglia were subjected to zymography for the assessment of MMP-2 and MMP-9. Increased amounts of MMP-9 and MMP-2 were observed in supernatants from LPS-treated astrocytes in comparison with supernatants from nontreated control cells. MMP-9 also increased in LPS-treated microglia. The treatment of astrocytes and microglia with IFN-beta inhibited dose-dependently the expression of both MMP-2 and MMP-9 in LPS-treated astrocytes and of MMP-9 in LPS-treated microglia. These results demonstrate a modulating effect of IFN-beta on the release of MMPs from CNS cells. This effect represents an additional mechanism by which IFN-beta, may decrease the development of new CNS lesions in the course of MS.