The epizootiology of epizootic haematopoietic necrosis virus (EHNV) was examined by experimental transmission and pathogenicity trials in the first known host species, Perca fluviatilis L., and 11 other introduced and native teleosts of Australia. Perca fluviatilis and four other species were highly susceptible to disease following bath exposure to EHNV. Three species developed disease only when inoculated by intraperitoneal injection, and four species were resistant to infection under the experimental conditions employed. Renal haematopoietic necrosis was the most consistent lesion produced, wit hepatic, splenic and pancreatic necrosis also occurring in certain species. The resistance of the virus to desiccation, disinfectants, high and low pH and temperature, and to prolonged storage at selected temperatures was assessed, demonstrating that the virus can survive for long periods in the aquatic environment and on fomites. Carrier individuals of P. fluviatilis, Salmo gairdneri Richardson, Maccullochella peeli (Mitchell), and possibly other teleosts, represent a further reservoir of infection. However, the virus could not be isolated from common insect and crustacean prey species, and no parasitic vectors were identified. It is proposed that EHNV has contributed to serious population declines of native species in recent decades, particularly of Macquaria australasica (Cuvier). Galaxias olidus Gunther and Bidyanus bidyanus (Mitchell). Salmonids are also known to be naturally and experimentally susceptible to the virus.