Summary Twelve human isolates exhibiting the properties of the family Pasteurellaceae but phenotypically deviating from established species, or resembling species of animal origin that are only rarely reported to occur in human materials, were checked for their identities by DNA-DNA hybridization. The collection consisted of one strain of Actinobacillus lignieresii , two strains of Actinobacillus hominis (mannose-positive), two hitherto undescribed Actinobacillus or Actinobacillus -like species, [ Pasteurella ] haemolytica biovar T, CDC group HB-5 (initially oxidase and indole-negative), a new species in the [ Haemophilus ] aphrophilus /[ Haemophilus ] segnis group, a new sucrose-negative and gas-producing Pasteurella -like species, and three strains of Bisgaard's Pasteurella -like taxon 16. Some diagnostically useful features of these unusual human Pasteurellaceae are described.