Yuhang District Maternity and Child Health Care Hospital 1 article published in JoVE Immunology and Infection Production of High-Titer Infectious Influenza Pseudotyped Particles with Envelope Glycoproteins from Highly Pathogenic H5N1 and Avian H7N9 Viruses Fengwei Zhang1, Yanan Wang2, Xuechai Shang1, Shanshan Wang1, Rong Xiao1, Hongjuan Zhou1, Long Cai1 1Central Laboratory, Hang Zhou Red Cross Hospital, 2Clinical Laboratory, Yuhang District Maternity and Child Health Care Hospital This protocol describes an experimental process to produce high-titer infectious viral pseudotyped particles (pp) with envelope glycoproteins from two influenza A strains and how to determine their infectivity. This protocol is highly adaptable to develop pps of any other type of enveloped viruses with different envelope glycoproteins.