Mandibles of 258 brown hares Lepus europaeus Pallas, 1778 from Poland were controlled for abnormal expression of the premolars. In four individuals a reciprocal transposition of the right and left third lower premolars was found. In addition, all the affected premolars were rotated. The rotation showed bilateral symmetry in each of the four specimens. A genetical basis is suggested for this type of tooth anomaly.