The activity of leucocytes isolated from the anetrior kidney of rainbow trout Oncorhynchus mykiss vaccinated with formalinkilled Vibrio anguillarum, β-haemolytic Streptococcus sp. or Renibacterium salmoninarum were investigated using the chemiluminesecnce (CL) assay. The vibrio and streptococcal bacterins were administrated by intraperitoneal injection or by the direct immersion method. The R. salmoninarum bacterin was inoculated intraperitoneally. The CL response of leucocytes from fish injected with vibrio or streptococcal bacterin was excellent against each opsonized bacterial cell. The leucocytes of each fish administrated by the immersion method also showed a high response level; however these emitted light levels were less than those of fish vaccinated by injection. The enhancement of CL response was not observed on the leucocytes of fish vacclnated with R. salmoninarum bacterin.