Ardeid birds and pigs are known as major amplifying hosts for Japanese encephalitis virus, and ducklings and chickens have been considered to play at best a minor role in outbreaks because of their low or absent viremia. We hypothesized that viremia of sufficient magnitude would develop in young ducklings (Anas platyrhynchos) and chicks (Gallus gallus) for them to serve as reservoir hosts and thereby contribute to the transmission cycle. Infection was associated with reduced weight gain in both species, and ducklings infected at 10 days of age or less showed overt clinical signs of disease. The mean peak viremia in birds of both species decreased as the age at infection increased from 2 to 42 days, indicating the importance of age of infection on magnitude of viremia in birds from both species, and suggesting that young poultry may be amplifying hosts of importance in disease-endemic regions.