This study investigates the involvement of mts1 (S100A4) in the metastatic process. We have evaluated the levels of mts1 gene in murine cancer cells following modulation of the metastatic ability. We report here that modulation of the expression of mts1 gene in cells derived from a breast murine adenocarcinoma (TS/A) did not correlate with metastatic ability either when pretreated in vitro with gamma-interferon (gamma-IFN) or following transfection with gamma-IFN gene. In another series of experiments we treated the cell lines B16-A and B78H1, both derived from B16 melanoma, with gamma-IFN. An increased expression of mts1 was found only in B16-A, but not B78H 1, correlated with a strong increase in metastatic activity of B16-A clone upon gamma-IFN treatment.