A cell line, FBM-17, was established from a fetal bovine thymus and passaged for more than a year. Electron microscopic examination revealed that the cytoplasm contained many phagosomes and a significant amount of rough endoplasmic reticula. In addition, FBM-17 cells showed non-specific esterase, phagocytosis and surface expression of Fc receptors for IgG and classes I and II MHC antigens. These observations confirmed that this cell line had the morphologic and functional features as a macrophage. MHC expression markedly increased by treatment with recombinant bovine gamma-interferon, showing the cell line to be sensitive to bovine gamma-interferon and functional. These present results suggest that the FBM-17 is a functional bovine macrophage cell line. This line gamma-interferon, showing the cell line to be useful for clarification of roles of macrophages in immunoregulation in cattle.