Additional methods of characterizing modes of virus inactivation were applied in studies of inactivation of CA9, EC7, and PO1 by ascorbic acid and sodium bisulfite (NaHSO 3 ) (Salo and Cliver 1978) . These studies had been prompted by Lynt's perception that sodium bisulfite in cole slaw had antiviral activity (Lynt 1966) . All the three viruses were susceptible to these food additives at levels of 0.1 M and sometimes much less (Salo and Cliver 1978) . Methods of characterizing virus degradation during inactivation included: loss of hemagglutinating activity (EC7 only); differential adsorption to cellulose nitrate (Millipore GSWP) and cellulose acetate (Gelman GA-8) filters; differential attachment to primate (HeLa) and non-primate (MDBK-bovine) cells; RNA infectivity of whole virus or cold phenol-extracted RNA as facilitated by DEAE-dextran; and sedimentation in sucrose density gradients. When whole virus was apparently inactivated, in that it could no longer initiate plaques, it was often infectious when inoculated together with DEAE-dextran, which showed that the viral RNA was intact. The native viruses were adsorbed by cellulose nitrate but not cellulose acetate filters, as reported previously (Herrmann and Cliver 1973c) ; however, PO1 labeled with 32 P-RNA and inactivated by 25 mM NaHSO 3 gradually developed affinity for the cellulose acetate membrane, as measured by retention of virus-associated radionuclide. 14 C-leucine labeled PO1 showed low nonspecific attachment for MDBK (bovine) cells: after inactivation, the virus had no more affinity for HeLa (human) cells than for MDBK. Much 32 P in PO1 inactivated by ascorbate no longer banded as native virus fraction in the sucrose density-gradient experiments; in one instance, EC7 (which has the same sedimentation profile) was mixed with the PO1 before centrifugation. EC7 hemagglutination identified the fractions that would contain native PO1. Some of these means of characterizing inactivated virus might be adaptable for use with molecular methods.