Homeopathic remedies have been selectively employed in human medicine since Hahneman introduced the concept in 1828. While the use of homeopathy is regionally popular in both human and veterinary medicine, there is still a significant lack of scientific evidence supporting its efficacy. This is likely due to an absence of studies evaluating the mechanism of action of these compounds. Engystol® an FDA-approved antiviral agent, is a popular homeopathic commercial product. In select in vivo and in vitro observational studies, the drug showed a measureable innate immune therapeutic efficacy. The focus of the present study was to evaluate the innate and adaptive immunomodulatory effects of oral Engystol(®) (1 or 10 tablets/L water consumed), prior to and post antigenic challenge in a mouse model with a well-characterized and clinically measureable immune system. We first evaluated the murine immune response when oral Engystol(®) was given alone for 28days. Mice were then challenged with an antigen-specific H5N1 HA vaccine while on Engystol(®) for an additional 33days. Serum and supernatants from cultured splenic lymphocytes were collected and screened with a 32-cytokine panel. Serum vaccine epitope-specific IgG titers plus T cell and B cell phenotypes from splenic tissue were also evaluated. Preliminary results showed that Engystol(®) alone did not alter immunity; however, upon vaccine challenge, Engystol(®) decreased CD4(+)/CD8(+) ratios, altered select cytokines/chemokines, and anti-H5N1 HA IgG titers were increased in the 10 tablet/L group. Collectively, these data suggest that Engystol(®) can modulate immunity upon antigenic challenge.