Background - Influenza viruses cause highly contagious acute respiratory illnesses with significant mortality, especially among young children, elderly people, and individuals with serious medical conditions. This encourages the development of new treatments for human flu. Biotherapies are diluted solutions prepared from biological products compounded following homeopathic procedures.Objectives - To develop a biotherapy prepared from the infectious influenza A virus (A/Aichi/2/68 H3N2) and to verify its in vitro response.Methods - The ultradiluted influenza virus solution was prepared in the homeopathic dilution 30dH, it was termed Influenzinum RC. The cellular alterations induced by this preparation were analyzed by optical and electron microscopy, MTT and neutral red assays. Glycolytic metabolism (PFK-1) was studied by spectrophotometric assay. Additionally, the production of tumor necrosis factor-α (TNF-α) by J774.G8 macrophage cells was quantified by ELISA before and after infection with H3N2 influenza virus and treatment.Results - Influenzinum RC did not cause cytotoxic effects but induced morphological alterations in Madin–Darby canine kidney (MDCK) cells. After 30 days, a significant increase (p < 0.05) in mitosis rate was detected compared to control. MDCK mitochondrial activity was changed after treatment for 10 and 30 days. Treatment significantly diminished (p < 0.05) PFK-1 activity. TNF-α in biotherapy-stimulated J774.G8 macrophages indicated a significant (p < 0.05) increase in this cytokine when the cell supernatant was analyzed.Conclusion - Influenzinum RC altered cellular and biochemical features of MDCK and J774G8 cells.