A hybridoma cell line that continually secretes antibody against infectious hematopoietic necrosis virus was developed and designated M-IHNV-W1. Antibodies in culture fluids were concentrated and purified by Protein A Sepharose CL-4B affinity chromatography. The immunoglobulin was isotyped as IgG 2b with a kappa light chain. The IgG was specific for infectious hematopoietic necrosis virus and had binding activity but low neutralizing activity. Little cross-reactivity occurred with viral hemorrhagic septicemia or infectious pancreatic necrosis viruses.