A 53-year-old male visited our hospital due to nasal obstruction persisting for 6 months and constant rhinorrhea. Pasteurella multocida subsp. multocida was isolated from his nasal discharge and lavage fluid of the maxillary sinus, and also from the oral cavity of the dog he kept. The bacterial strains isolated from the patient and dog were identical in terms of biochemical properties, and drug sensitivity. Although serotype was different, the strain from the patient showed (A:6) and that from his dog showed (A:5). The microorganism is not present in the general environment. The patient had contact with his dog such as he kissed it frequently, gave it food with his chopsticks et al.. From the mouth of the people who kiss one's dog, we detected Pasteurella of the same character of bacteria as from the mouth of the dog. We detected two Pasteurella multocida of different character from only one mouth of a cat. Pasteurella multocida was checked in only one colony for sero type. Sero type A is the popular type for dogs and cats. The above suggest that their was a high possibility that the Pasteurella multocida subsp. multocida found in the patient was from his dog. In Japan, the incidence of Pasteurella multocida subsp. multocida infection has been increasing. In 1969, the Japanese Ministry of Health and Welfare officially communicated this infection as a zoonosis to related institutions. At both medical and surgical departments, wither the patient keeps a pet should be confirmed during interview, and guidance of pet keeping methods is important in some cases from the aspect of clinical bacteriology.(ABSTRACT TRUNCATED AT 250 WORDS)