This work details the location and movement of the major influenza virus proteins throughout the process of infection. The first section documents and analyzes the fate of proteins from the input virus on infection at 4° and on subsequent incubation at 37°. The second section describes the appearance and movement of newly synthesized viral proteins both into and out of the nucleus, and details the release of virions and viral components into the tissue culture fluids. The third section investigates the state of newly synthesized viral proteins within both nucleus and cytoplasm. The appendix reviews the methods of cell fractionation and their criteria of purity.