Newcastle disease is a highly contagious and sometimes fatal illness affecting poultry. The severity of the disease is a function of the virulence of the infecting viral strain. Lentogenic strains infect the trachea, lungs and air sacs, and interfere with egg production. Mesogenic and velogenic strains are manifested through incoordination, paralysis, swelling of tissue around the eyes, diarrhea and eventual death. An assessment of immune status, as well as serological identification of Newcastle disease virus (NDV), requires a measurement of antibody to NDV in serum. Enzyme-linked immunosorbent assay (ELISA) systems have proven efficacious in the quantification of antibody levels to NDV, and facilitate the monitoring of immune status in large flocks.