A series of avian orthomyxoviruses and paramyxoviruses were cocultivated in embryonated chicken eggs. This resulted in two categories of behavior being observed: (i) one virus was preferentially detected over the other, as shown by five out of six influenza A viruses of differing hemagglutinin subtypes being preferentially detected over paramyxoviruses, and (ii) dual isolations, for example, dual isolations of paramyxoviruses. These findings are considered in the light of results of surveillance studies of orthomyxoviruses and paramyxoviruses carried out on domestic poultry in Hong Kong.