Problems with high mortality of newly metamorphosed halibut (Hippoglossus hippoglossus) fry has slowed the development of commercial production and infectious pancreatic necrosis virus (INV) is believed to be one of the causes of this mortality. To clarify a possible relationship between IPNV and the mortality, fry were challenged by i.p. injection with IPNV. Significant differences in the mortality were found between the fish i.p. injected with IPNV (53.6%) and the control fish (8.5%), indicating that IPNV is pathogenic to the fry. Challenged halibut responded to IPNV infection by a rise in the level of IPNV-specific antibodies from 26 to 42 days post challenge.