Using the rapid glass plate method, the Newcastle disease virus strain MET95 showed much weaker haemagglutination (HA) activity for chicken erythrocytes than 69 other Newcastle disease viruses, including 56 field strains isolated from chickens reared in Japan between 1988 and 2001. Using erythrocytes from other avian species, only the MET95 strain failed to show HA activity for erythrocytes from ducks, geese or pigeons. The haemagglutinin-neuraminidase protein of the MET95 strain was shown to have unique substitutions of isoleucine for thereonine and leucine at amino acide residues 216 and 552. It is suggested that these two substitutions might relate to the unique HA activity of the MET95 strain. This HA activity may be a useful marker for this strain.