A reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) assay was evaluated to monitor infectious hematopoietic necrosis virus (IHNV) from artificially infected rainbow trout Oncorhynchus mykiss. The cumulative mortalities of fish challenged with IHNV at 106.5 TCID50/fish, 105.5 TCID50/fish and 104.5 TCID50/fish were 40%, 0% and 0%, respectively. Dead fish and survivors at 16 and 28 d post-challenge in each group were employed for IHNV detection by RT-LAMP assay and virus isolation using BF-2 cells. IHNV from 104.3 to 106.8 TCID50/㎖ was isolated from all the dead fish and also detected in all of the examined dead fish by RT-LAMP assay. In survivors at 16 d, 60% (3/5 fish, 102.8-105.05 TCID50/㎖), 20% (1/5 fish, 101.05 TCID50/㎖) and 60% (3/5 fish, 101.05-104.8 TCID50/㎖) were found to be IHNV-positive by virus isolation in fish challenged with IHNV at 106.5 TCID50/fish, 105.5 TCID50/fish and 104.5 TCID50/fish, respectively, while 20% (1/5 fish), 0% (0/5 fish) and 20% (1/5 fish) were IHNV-positive by RT-LAMP assay. No IHNV was detected in the survivors at 28 d and control fish. These results indicate that the RT-LAMP assay is useful for detection of IHNV in diseased fish although it is not enough to monitor virus in IHNV-survivors.