IFN-gamma is an important regulator of immune responses and inflammation. Studies in animal models of inflammation, autoimmunity, cancer, transplant rejection and delayed-type hypersensitivity have indicated that administration of antibodies against IFN-gamma can prevent the occurrence of diseases or alleviate disease manifestations. Therefore, it is speculated that such antibodies may have therapeutical efficacy in human diseases. Since animal-derived antibodies are immunogenic in patients several strategies are being developed in order to reduce or abolish this human anti-mouse antibody (HAMA) response. In our laboratory, we have constructed a single-chain variable fragment (scFv) derived from a mouse antibody with neutralizing potential for human IFN-gamma. A scFv consists of only variable domains tethered together by a flexible linker. The scFv was demonstrated to neutralize the antiviral activity of HuIFN-gamma in vitro and therefore might be considered as a candidate for human therapy.