The gene encoding the ferric uptake regulator protein (fur gene) of Vibrio salmonicida 87/09/1193 was located following hybridisation of an EcoRI digest of chromosomal V. salmonicida DNA with a 316 base pairs (bp) probe internal to the fur gene of Vibrio anguillarum. A 2088 bp fragment including an open reading frame of 441 bp, encoding a protein of 147 amino acids, and homologous with fur, was identified, cloned and sequenced. A plasmid bound V. salmonicida fur gene was found capable of complementing the fur mutation of Escherichia coli H1681. Although no 'iron-box' was identified upstream of the start-codon, beta-galactosidase activity in E. coli H1681 was regulated by iron availability in the media, indicating that in V. salmonicida fur, as in other fur genes, iron functions as a co-repressor. Southern blot hybridizations demonstrated that fur is conserved amongst V. salmonicida strains and several other closely related Vibrio strains in which fur remains as yet, uncharacterized. The fur gene of Vibrio logei NCIMB 2252 was subsequently amplified using polymerase chain reaction primers external to the V. salmonicida fur gene. Comparison of phylogenetic analyses using fur and 16S DNA coding for rRNA sequences, confirmed the usefulness of fur as an evolutionary marker within the genus Vibrio.