The Kerr effect causes a nonreciprocity between the two counterpropagating lightwaves in the fiber coil of a fiberoptic gyro, thus resulting in a spurious rotation signaI. For interferometric fiber gyros, a power difference as small as ten nanowatts gives a rotation error which is too large for inertial navigation. In this paper, we describe properties of the Kerr effect as observed in a Brillouin fiber-optic gyro (BFOG).