For influenza hemagglutination inhibition (HAI) assays, species selection of red blood cells (RBCs) is critical to determine antibody titers to influenza viruses reliably. We compared pandemic influenza virus A/H1N1 (pdH1N1) HAI titers using turkey or guinea pig RBCs. Turkey RBCs appear to be the more appropriate species choice for influenza A/pH1N1 HAI assays.