A recombinant therapeutic agent which is chemically identical to or similar to the endogenous lymphokine interferon gamma (IFN-gamma) with antineoplastic, immunoregulatory, and antiviral activities. Therapeutic IFN-gamma binds to and activates the cell-surface IFN-gamma receptor, stimulating antibody-dependent cytotoxicity and enhances natural killer cell attachment to tumor cells. This agent also activates caspases, thereby inducing apoptosis in malignant cells.