Moderate positive correlations for all groups were found between the peak virus titre shed and the number of lung MNCs secreting influenza-specific IFN-γ (R +0.5775, P 0.0096), and the total amount of virus shed by ferrets and the number of lung MNCs secreting influenza-specific IFN-γ (R +0.5870, P 0.0082). The gene discussed is IFNG; the disease is influenza.