Determination of CPE during these experiments revealed that the double glycoprotein-avianized virus only produced CPE at 72 hrs pi when experiments were performed at 37uC, whereas wild-type human virus produced CPE earlier and at both temperatures (data not shown). These data are consistent with the levels of CPE observed for A/Dk/Eng/62 (H4N6) and A/ Victoria/3/75 (H3N2) in our initial studies ( Figure 1B) and suggest that altering the human virus glycoproteins to avian virus-like characteristics has profound effects on infection, spread and CPE in the environment of the human ciliated airway epithelium.