The relationships between the plasma parameters downstream and upstream of plane wave rotational discontinuities (RDs) are reanalyzed for the case of an isotropic plasma. The analysis is carried out in the rest frame of the RD using a Cartesian coordinate system with axes labeled n, j, and z. The NJZ system is oriented in such a way that the n axis is parallel to the RD surface normal vector and the j component of B is the same on both sides of the RD. In this NJZ system the magnitude of each of the downstream components of B, U,and E is equal to the magnitude of the respective upstream components, and the sign of Bz, Uz, and En changes across the discontinuity. In the NJZ system the angle through which the tangential component of the magnetic field (Bt) rotates is not arbitrary. It depends explicitly on the angle between the upstream Bt and the j axis. The above jump relations can be used to simplify initial conditions used in theoretical and simulation studies of RD structure. The jump relations can also be used, in principle, to provide an additional method for determining the direction of the RD surface normal vector from spacecraft data. ¿ American Geophysical Union 1993