Representatives of paramyxoviruses isolated from waterfowl in the U.S.A., goose/Delaware/1053/76, and Japan, pintail/Wakuya/20/78, were shown to be serologically closely related but distinct from other avian paramyxoviruses. Another isolate, from domestic ducks in the U.S.A., was shown to be representative of a further distinct serotype of avian paramyxoviruses. We propose that, in the current system of nomenclature these serotypes be designated PMV-8, for which the prototype strain would be PMV-8/goose/Delaware/1053/76 and PMV-9, for which the prototype strain would be PMV-9/domestic duck/New York/22/78.