Within the framework of highly pathogenic avian influenza (HPAI) surveillance in Vietnam, interviews were carried out with poultry breeders and local animal health operators in 2 communes of the Red River Delta (RRD) with a view to documenting the circulation of sanitary information concerning poultry and the economic and social incentives for disseminating or withholding information. The main results demonstrate that (1) active "informal" surveillance networks exist, (2) the alert levels vary and the measures applied by the breeders are myriad and often far-removed from the official recommendations and (3) the commune veterinarian represents an interface between the formal and informal systems.