Juvenile rainbow trout (Oncorhynchus mykiss) acclimated to fresh water or salinities of less than or equal to 9.0parts per thousand were exposed orally or by immersion to Yersinia ruckeri. Immersion or oral exposure affected the survival of fish. All deaths occurred between 4 and 12 d after exposure to Y. ruckeri. Analysis of variance indicated that mortalities of fish exposed by immersion were significantly lower in higher salinity. However, mortalities following oral uptake was significantly lower in fresh water and 1.0parts per thousand salinity than in 3.0 and 9.0parts per thousand salinity. Survival of the orally exposed fish in fresh water and 1.0parts per thousand salinity was significantly lower than that of immersion-exposed fish. However, when the data were analyzed by Kaplan-Meier survival and failure time analysis there was no significant difference found among salinities in either group.