Abstract
JJ/50 and four other strains of influenza C virus grew in an established line of canine kidney (MDCK) cells. Multicycle virus growth was markedly enhanced by the addition of trypsin to the culture medium and these viruses could be passaged serially in this system. The addition of appropriate concentrations of trypsin to the agar overlay medium enabled plaquing of influenza C/JJ/50 virus. Titration by plaque assay on MDCK cells was more sensitive than that by intra-amniotic inoculation of fertile hens' eggs.