Malsberger, R. G. (Lehigh University, Bethlehem, Pa.), and C. P. Cerini. Characteristics of infectious pancreatic necrosis virus. J. Bacteriol. 86:1283-1287. 1963.-Infectious pancreatic necrosis virus of trout is an ether-stable virus unable to cause hemagglutination or hemadsorption. During multiplication, the latent period was 5 hr and was followed by a logarithmic phase of virus release terminating at 12 hr postinfection. The virus yield per infected cell averaged 300 tcid(50). Autointerference was demonstrated on serial passage of undiluted seed virus. Infectivity was maintained on storage at 4 C for approximately 5 weeks after which the loss of infectivity became exponential. At -70 C, the decrease in infectivity was exponential through 36 weeks with a total loss of approximately 0.5 log(10) units. The virus is antigenic, and cross-neutralization occurred between the original isolate and a feral strain isolated from tissue cultures of apparently normal trout. The reported characteristics, together with the known size of 30 mmu, are all consistent with the characteristics of the Picornavirus group.