Influenza virus strain A/Aichi/2/68 replicated only in the lungs, nasa
l cavity, and trachea after intranasal challenge of white mice weighin
g 14-16 g. Rapid accumulation of the virus was associated with a somew
hat delayed accumulation of endogenous interferon in the lungs, the co
ncentration of interferon gradually decreasing by the end of the disea
se. An appreciable accumulation of the virus in the nasal cavity was c
oupled with weak interferon induction in this organ. On the other hand
, a high level of interferon in the blood was concomitant with the dev
elopment of slight sporadic viraemia.