Replicas from complementary freeze-fracture faces of the rabbit rod outer segments were examined in an electron microscope. By this method two dissimilar faces, A and B, were visualized in a disc. The A face, toward the intradisc space, was characterized by densely packed particles, about 10 nm in diameter, rising on it; and the B face, toward the interdisc space, appeared smooth with minute unevennesses. An A face always formed a complementary set with a B face, and vice versa. No evidence has been obtained to suggest that a disc membrane may split along two or more different fracture planes.