In a 4-year study (1980-1983) involving the use of sentinel ducks that intermingled with wild ducks, a total of 98 paramyxovirus (PMV) isolates (84 Newcastle disease virus, 14 PMV-6) were obtained from 3652 sentinel duck cloacal samples (2.7% isolation rate) collected between June and mid-November each year. PMV infection of sentinel ducks appeared to be seasonal, with the onset of infection occurring between mid-July and mid-August. PMV was not isolated from sentinel turkeys that co-mingled with sentinel ducks during the last 2 years of the study. However, there was serological evidence that the sentinel turkeys were infected with PMV. These findings indicate that wild waterfowl are a natural reservoir of PMV and suggest that interspecies transmission of certain PMV serotypes may occur between waterfowl and turkeys.