Localization of Pasteurella pneumotropica was investigated in the respiratory tract, conjunctiva and vagina of 5-week-old, 10-week-old and retired asymptomatic mice and rats. The highest isolation rate of the organisms was obtained in the pharyngolarynx, showing 85 to 97.5% in carrier mice and 100% in carrier rats. Numbers of the organisms in this site were 10(3-5) and 10(7-8) organisms/g tissue in 4-week-old mice and rats, respectively. Isolation rates in the nasal cavity and trachea of the both animals were not so high as those in the pharyngolarynx, but usually higher than those in the external nares. The organisms were rarely isolated from the lung. Isolation of the organisms from the conjunctiva was common in rats, especially in young ones, but rare in mice. About 30% of carrier mice and 50 to 100% of carrier rats harbored the organisms in their vaginas.