Ulcerations of the skin associated with haemorrhagic petechiae of liver and kidneys, were the main signs of disease affecting salmon and brown trout in Norway. A death rate of 15–20% was estimated for the 5 month period of mid‐March‐August, although mortalities occurred throughout the year. Bacteriological examinations, involving 36 isolates, suggested the causual organism to be aPasteurellaalthough the DNA homology examination gave a G.C. ratio of 55.6 % which is high forPasteurellaas a