The karyotypes of the rainbow trout (Salmo gairdneri R.) and the brown trout (Salmo trutta L.) were analyzed by means of silver staining and the chromomycin A3/distamycin A/DAPI fluorescence banding technique. The nucleolus organizer regions (NORs) were localized at the secondary constrictions of chromosome no. 14 in S. gairdneri and of chromosome no. 10 in S. trutta. Additional silver positive dots were observed at or close to several centromeres in S. gairdneri. Brilliant chromomycin A3 (CMA3) fluorescence heterochromatin blocks were localized on both sides of the nucleolar constrictions in S. gairdneri. A polymorphic CMA3 positive band was detected close to the NORs of S. trutta. No distamycin A/DAPI intense heterochromatin blocks were detected in the genomes of the two Salmo species investigated.