Abstract.The effectiveness of three different growth media KDM‐2, S‐KDM and S‐KDM‐C for primary isolation ofRenibacterium salmoninarumwas examined over a 14‐week incubation period. Kidney samples were taken from Atlantic salmon,Salmo salarL., broodfish returning to a sea ranch after 2 years at sea. Homogenized samples were inoculated onto two selective media, S‐KDM supplemented with lamb serum and S‐KDM‐C supplemented with activated charcoal. The third medium was the non‐selective serum supplemented KDM‐2.Renibacterium salmoninarumwas isolated from 112 samples on one or more of the media used. Of all positive samples, 91% were positive on S‐KDM, 60% on S‐KDM‐C and 35% on KDM‐2. These results demonstrate that selectivity significantly enhances the isolation capacity of the medium and that supplementing with serum is significantly more effective than