The article reviews the literature with regard to identification of lymphocyte subsets that respond to specific inducers and produce IFN-gamma, the structure of IFN-gamma gene, the IFN signal transduction pathway that initiates biochemical changes at cellular level and influences the function of immunocompetent cells: mononuclear phagocytes, T and B lymphocytes. The interaction of IFN-gamma with other cytokines in regulation of immune response is also discussed.