A new rat mutant with abnormal behavior has been found in a closed colony of Slc: SD. The affected rats turned around after their own tails beginning 4-5 weeks after birth, in response to extroceptive stimuli, such as sound or vibration. The behavior was more pronounced in younger animals. On gross observation, no alteration was found in the cerebrum, cerebellum, or anterior, posterior, or lateral semicircular canals. Light microscopic examination revealed no abnormality in the cerebrum or cerebellum. The trait was controlled by an autosomal dominant gene with incomplete penetrance (78.0%) when transferred to the WKY genetic strain background. It was named "turning" with the gene symbol Tur. A congenic strain was established, which was designated WKY/Eis-Tur.