The sequences of gene segments 2 and 8 from 10 different isolates of infectious salmon anaemia virus (ISAV) sampled in Norway, Canada and Scotland between 1987 and 1999 were determined and compared. Pairwise comparisons revealed a high degree of homology between the European isolates, with identities of 98 to 100% for both genes examined. The Canadian isolate showed identities of 84 and 87 to 88% with the European isolates for the nucleotide sequence of segments 2 and 8, respectively. Phylogenetic analyses were performed to establish the interrelationship between the European virus isolates. The evolutionary rate based on 4 Norwegian isolates clustered together in the analysis of segment 2 was calculated to be 0.96 x 10(-3) nucleotides site(-1) yr(-1). On the basis of this mutation rate it was estimated that the Norwegian Glesvaer 90 and Canadian Bay of Fundy 97 isolates diverged around 1900, which coincides with transportation of salmonids between Europe and North America starting in the late nineteenth century.