An influenza A virus isolated from a duck during a recent surveillance study on commercial poultry from the People's Republic of China and the New Territories, Hong Kong, was shown to possess Hswl antigens related to that of the swine (Hsw1N1) influenza virus. The isolation of an Hsw1N1 influenza virus from ducks indicates that avian species, as well as pigs, may serve as a reservoir of this potential pathogen for humans. The virus was avirulent for ducks, turkeys, chickens, and pigs.