Erythrocytic inclusion body syndrome (EIBS) was artificially established in selected stocks of juvenile fall and spring chinook salmon (Oncorhynchus tshawytscha), chum salmon (0. keta), coho salmon (0. kisutch), Atlantic salmon (Salmo salar), and rainbow trout (0. mykiss). Adult spring chinook salmon were also artificially infected with the EIBS virus. Adult male chinook had higher prevalences of EIBS inclusion bodies than females. Cytoplasmic inclusion bodies that are associated with EIBS were not observed in steelhead (0. mykiss), brown (Salmo trutta) nor brook (Salvelinus fontinalis) trout suggesting that these stocks are less susceptible to the EIBS virus. Coho salmon with EIBS were more susceptible to Flexibacter psychrophilus, the causative agent of cold water disease (CWD) than fish without EIBS. The fish with EIBS were most susceptible to F. psychrophilus during the first 20 days after virus exposure, when inclusion bodies were most prevalent. Coho salmon infected with both the EIBS virus and F. psychrophilus required a longer recovery period than fish exposed to either pathogen alone. Most investigations of EIBS require in vivo experimentation and artificial infections using diseased fish tissues. Heterologous tissue used to establish EIBS did not contribute to anemia nor mortality. Death was not attributed to the EIBS virus alone but to the combined effects of the virus and a secondary pathogen. The severity of EIBS may be reduced with dietary Vitamin C prophylaxis. Fish fed 1,000 mg ascorbic acid/ Kg of diet had the fewest signs of EIBS; they had the highest hematocrit values and the lowest incidence of cytoplasmic inclusion bodies. However, vitamin C therapy alone was not sufficient to prevent the disease. / Graduation date: 1992