Bacteria of the avian [Pasteurella haemolytica]-'Actinobacillus salpingitidis' complex have been associated with different pathological conditions in birds, among which salpingitis and peritonitis in chickens of layer type seem to dominate. The aim of this study was to classify these bacteria by comparison of 37 strains tentatively classified as biovars of the avian [P. haemolytica]-'A. salpingitidis' complex or as Pasteurella anatis. PFGE, AFLP and plasmid profiling showed that strains representing different biovars were genotypically different. Phylogenetic analysis of 22 strains characterized by 16S rRNA gene sequence comparison showed that strains classified as biovars 5, 8 and 9 were closely related to the suggested type strain of 'A. salpingitidis' (98.4-99.9% similarity), whereas the remaining strains classified in 12 biovars or as P. anatis were closely related to the type strain of P. anatis (98.1-100% similarity). The two groups were related at 95.7-97.1% similarity. The closest similarity outside this group was 94.6%, between biovar 15 and Bisgaard taxon 3. DNA-DNA hybridization was performed with 34 strains and showed binding above 85% for strains of biovars 5 and 8, including the suggested type strain of 'A. salpingitidis'. Two strains of P. anatis (F 149T and F 279) were closely related at 79% DNA binding to 27 strains of biovars 1,3, 4, 11, 12, 17-20, 22 and 24. A new genus, Gallibacterium gen. nov., is proposed to include the avian [P. haemolytica]-'A. salpingitidis'-P. anatis complex, since these taxa form a monophyletic unit with similarities above 95% on the basis of 16S rRNA sequence comparison and they are unrelated to other genera of the family Pasteurellaceae Pohl 1981. The new genus consists of Gram-negative, non-motile, rod-shaped or pleomorphic bacteria. The bacteria are catalase-, oxidase- and phosphatase-positive. Nitrate is reduced and acid is produced without gas formation from glycerol, (-)D-ribose, (+)D-xylose, (-)D-mannitol, (-)D-fructose, (+)D-galactose, (+)D-glucose, (+)D-mannose, sucrose and raffinose. The genus Gallibacterium can be separated from other genera of Pasteurellaceae by differences in catalass, symbiotic growth, haemolysis, urease, indole, acid production from (+)D-xylose, (-)D-mannitol, (-)D-sorbitol, (+)D-mannose, maltose, raffinose and dextrin and ONPG and PNPG tests. Pasteurella anatis Mutters et al. 1985 is transferred to the new genus as Gallibacterium anatis gen. nov., comb. nov. Genomospecies 1 of Gallibacterium is proposed to include the former biovars 5 and 8 of the avian [P. haemolytica]-'A. salpingitidis' complex. The type strain of Gallibacterium anatis is F 149T (=ATCC 43329T = NCTC 11413T) and the reference strain of Gallibacterium genomospecies 1 is CCM 5974.