Abstract
The infection of eggs, cell cultures or mice with a mixture of amantadine-resistant and amantadine-sensitive strains of influenza virus resulted in the transfer of amantadine-resistance or sensitivity between strains. The response of a recombinant virus to amantadine was not related to either of its surface antigens. Resistance to amantadine was transferred as an all-or-none character. It is concluded that amantadine-resistance is a useful genetic marker for influenza viruses.