Enriched human interferon-γ (HuIFN-γ) receptor preparations were obtained by affinity chromatography of non-ionic detergent solubilized COLO 205 cell membranes on immobilized recombinant HuIFN-γ. The active fractions, identified by a competition ELISA, were used as the immunogen in a BALB/c mouse. Fusion of its splenocytes with myeloma cells yielded several hybrids secreting antibodies that inhibit the antiviral activity of HuIFN-γ; the two most active ones were selected for further characterization. This blocking activity was restricted to both the human species and the γ type of IFN. Affinity purification of cell membrane extracts on the immobilized monoclonal antibodies resulted in the visualization of a major protein band with an Mr of 90,000, which is in good agreement with the results obtained by other authors [Aguet M. and Merlin G. (1987) J. exp. Med. 165, 988-999; Novick D., Orchansky P., Revel M. and Rubinstein M. (1987) J. biol. Chem. 262, 8483-8487; Sheehan K. C. F., Calderon J. and Schreiber R. D. (1988) J. Immun. 140, 4231-4237]. © 1990.