Virusys has developed a highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) for the detection of influenza A NP-specific antibodies in serum from human and veterinary sources. Because the assay utilizes "inhibition of binding" technology, it may be used with serum from any species, and therefore does not require speciesspecific conjugates. The assay can be completed in less than 1.5 hr., contains only one wash step, and incorporates proprietary diluents that are designed to prevent the development of nonspecific signal derived from sample matrix and/or the nonspecific adsorption of reactive test components.