Influenza is a contagious respiratory disease causing mild to severe illness. The emergence of a new Influenza virus H1N1 pandemic stain in 2009 has increased the risk of another pandemic. Some concern regarding the potential resistance to neuraminidase inhibitors, along with concerns regarding a readily available vaccine to target emerging viruses, and insufficient evidence to recommend use of antibiotics for upper respiratory tract infection (Aroll B et al, 2005), have motivated researchers to look for alternative medicines and other therapies including herbal remedies. Plants species belonging to Genus Echinacea are among the most extensively used herbal remedies for "flu- like" symptoms, and are also known to be used traditionally in North Americans native populations for respiratory illness, wounds, digestive problems, and poisoning (Felter et al., 1983, Hobbs, 1994). Recent research on Echinacea species has been primarily focused on the immune modulatory properties, particularly in preventing and treating respiratory tract infection (Barnes et al., 2005). Several studies using Echinacea extract treatments have reported beneficial effects in preventing and treating respiratory tract infections such as influenza or rhinovirus infections, but the efficacy of Echinacea is debatable due to inconsistent findings. In this dissertation, we report the results of investigation into the effect of different extracts prepared from two commonly used Echinacea species, E. angustifolia and E. purpurea. The in vivo disease model used to test the efficacy of these extracts is a murine model of influenza infection. Both aqueous and ethanol extracts from E. angustifolia and E. purpurea were tested in mice subsequently infected with influenza virus. All extracts tested harbored some level of immune modulatory potential, but showed large variability based on plant species and extraction method used. Aqueous extracts from both species of Echinacea demonstrated greater stimulatory effects on immune responses than did ethanol extracts. The most striking effects were improved survival rate and increase in wide range of cytokine/chemokines in the lungs by water extracts. With respect to a species effect, E. angustifolia extracts tended to have more potent activity than E. purpurea extracts and this held true for both water and ethanol extracts. Modulation of specific cell populations in the lung was also found, but this effect varied by type of extract. In spite of these immunomodulatory changes, there was no reduction in the lung viral load, or any change in weight loss or food intake up to day 8 post-infection.