Very early in my tenure with FRI, I was invited to review knowledge of irradiation of viruses, as it might pertain to food preservation (Cliver 1965b) . Some irradiation-inactivation results were presented at the 1965 water symposium, but these were not for viruses that were likely to be foodborne (Sharp 1967) . Picornaviruses and caliciviruses present extremely small targets and are thus likely to require large doses of ionizing irradiation to achieve substantial degrees of inactivation (Kaplan and Moses 1964) . Predictability of ''kills'' is further complicated by the tendency of viruses to aggregate, whereby an infectious unit may comprise two or more virions, all of which must be inactivated before the infectivity of the unit is lost Chang 1967) . Studies we did with support from the US Atomic Energy Commission seemed to indicate that a low dose of 60 Co gamma-rays had induced both a host range and an antigenic mutation in CA9 (Cliver 1968 ), but the results were not repeatable. We later learned that CA9 was rather idiosyncratic among enteroviruses (Herrmann and Cliver 1973a ). More extensive virus irradiation studies were conducted in the Virology Branch of the US Food and Drug Administration (FDA- Sullivan et al. 1971) , who later reported that radiation sensitivity was lower in ground beef than in cell culture medium (Sullivan et al. 1973) .