We compared the receptor specificity of Newcastle disease viruses from a variety of avian species, including chickens and wild waterfowl, using hemagglutination tests with erythrocytes from different animal species. All isolates from wild waterfowl agglutinated horse erythrocytes, while the chicken isolates did not. The results showed that the receptor specificity of Newcastle disease viruses is different, depending on the avian species from which the viruses are isolated.