Pomegranates have high levels of polyphenols (PPs) and may be a rich source of compounds with antiviral activity. We evaluated the direct anti-influenza activity of three commercially available pomegranate extracts: pomegranate juice (PJ), a concentrated liquid extract (POMxl), and a 93% PP powder extract (POMxp). The acidity of PJ and POMxl solutions contributed to rapid anti-influenza activity, but this was not a factor with POMxp. Studies using POMxp showed that 5min treatment at room temperature with 800mug/ml PPs resulted in at least a 3log reduction in the titers of influenza viruses PR8 (H1N1), X31 (H3N2), and a reassortant H5N1 virus derived from a human isolate. However, the antiviral activity was less against a coronavirus and reassortant H5N1 influenza viruses derived from avian isolates. The loss of influenza infectivity was frequently accompanied by loss of hemagglutinating activity. PP treatment decreased Ab binding to viral surface molecules, suggesting some coating of particles, but this did not always correlate with loss of infectivity. Electron microscopic analysis indicated that viral inactivation by PPs was primarily a consequence of virion structural damage. Our findings demonstrate that the direct anti-influenza activity of pomegranate PPs is substantially modulated by small changes in envelope glycoproteins.