Abstract
Seventeen strains of yellow fever virus were compared by immunoblotting using polyclonal and monoclonal antibodies. Strains originating in South America were readily distinguishable from African strains on the basis of differences in the envelope protein. The 17D vaccine strain and strains derived from it differed radically from the parent Asibi and other wild-type strains in that cells infected with 17D did not accumulate intact envelope protein. We suggest that failure to accumulate the major viral surface protein is due to its increased susceptibility to breakdown and that this property may be a contributing factor in the attenuation of the vaccine strains.