Twenty-seven apparent paramyxoviruses, unrelated to known avian paramyxoviruses, were isolated at a Hong Kong dressing plant from the trachea or cloaca of birds originating from Hong Kong and the People's Republic of China. A total of 2443 apparently healthy ducks, geese and fowls was sampled and isolation frequencies were 1.3%, 1.0% and 0.5% respectively. Twenty of the isolates were from the cloaca; 11 were obtained in association with Newcastle disease virus and one with an avian influenza virus. The majority of the isolations were made in the winter months. All 27 isolates were serologically related although 11 representative isolates differed slightly in haemagglutinin properties. A representative isolate was not pathogenic for chickens. A serological survey of poultry indicated a relatively low incidence of infection.