A Taiwan AIV H 6 N 1 strain, 2838V (virulent), was obtained by serial inoculation of an original field isolate, H 6 N 1 2838, into specific pathogen free (SPF) chickens [36] . The virus was further amplified by passage into the amnion of SPF eggs. Cell debris in the collected fluid was clarified by centrifuging at 1000 rpm for 10 min and passing through a 0.45 mm filter. The viral titer (50% of the egg infectious dose, EID 50 ) of 2838V was 1610 8 /ml.